UNITS(1)							      UNITS(1)



NAME
       units — unit conversion and calculation program

SYNOPSIS
       'units' [options] [from-unit [to-unit]]

DESCRIPTION
       The 'units' program converts quantities expressed in various systems of
       measurement to their equivalents in other systems of measurement.  Like
       many  similar  programs, it can handle multiplicative scale changes. It
       can also handle nonlinear conversions such as  Fahrenheit  to  Celsius.
       See  the examples below.  The program can also perform conversions from
       and to sums of units, such as converting between meters and  feet  plus
       inches.

       Beyond  simple  unit conversions, 'units' can be used as a general-pur‐
       pose scientific calculator that keeps track of units  in  its  calcula‐
       tions.	You  can  form	arbitrary  complex mathematical expressions of
       dimensions including sums, products, quotients, powers, and even  roots
       of  dimensions.	 Thus  you can ensure accuracy and dimensional consis‐
       tency when working with long expressions that  involve  many  different
       units that may combine in complex ways.

       The units are defined in an external data file.	You can use the exten‐
       sive data file that comes with this program, or you  can  provide  your
       own  data file to suit your needs.  You can also use your own data file
       to supplement the standard data file.

       Basic operation is simple: you enter the units that you want to convert
       from  and  the units that you want to convert to.  You can use the pro‐
       gram interactively with prompts, or you can use	it  from  the  command
       line.

       You  can  change  the  default behavior of 'units' with various options
       given on the command line. See Invoking Units for a description of  the
       available options.

INTERACTING WITH UNITS
       To invoke units for interactive use, type 'units' at your shell prompt.
       The program will print something like this:

	  Currency exchange rates from 04/23/12
	  2516 units, 85 prefixes, 65 nonlinear units

	  You have:

       At the 'You have:' prompt, type the quantity and  units	that  you  are
       converting  from.   For	example,  if you want to convert ten meters to
       feet, type '10 meters'.	Next, 'units' will  print  'You  want:'.   You
       should  type the units you want to convert to.  To convert to feet, you
       would type 'feet'.  If the 'readline' library was compiled in then  the
       tab  key  can  be used to complete unit names. See Readline Support for
       more information about 'readline'.  To quit the program press Ctrl-C or
       Ctrl-D under Unix.  Under Windows press Ctrl-Z.

       The  answer  will  be displayed in two ways.  The first line of output,
       which is marked with a '*' to indicate multiplication, gives the result
       of the conversion you have asked for.  The second line of output, which
       is marked with a '/' to indicate division, gives  the  inverse  of  the
       conversion  factor.   If  you  convert  10 meters to feet, 'units' will
       print

	      * 32.808399
	      / 0.03048

       which tells you that 10 meters equals about 32.8 feet.  The second num‐
       ber  gives  the conversion in the opposite direction.  In this case, it
       tells you that 1 foot is equal  to  about  0.03	dekameters  since  the
       dekameter is 10 meters.	It also tells you that 1/32.8 is about 0.03.

       The  'units'  program prints the inverse because sometimes it is a more
       convenient number.  In the example  above,  for	example,  the  inverse
       value  is  an  exact  conversion: a foot is exactly 0.03048 dekameters.
       But the number given the other direction is inexact.

       If you convert grains to pounds, you will see the following:

	  You have: grains
	  You want: pounds
		  * 0.00014285714
		  / 7000

	  From the second line of the output you can immediately  see  that  a
       grain  is equal to a seven thousandth of a pound.  This is not so obvi‐
       ous from the first line of the output.  If you find  the output	format
       confusing, try using the '--verbose' option:

	  You have: grain
	  You want: aeginamina
		  grain = 0.00010416667 aeginamina
		  grain = (1 / 9600) aeginamina

       If  you	request  a  conversion	between  units that measure reciprocal
       dimensions, then 'units' will display the conversion  results  with  an
       extra note indicating that reciprocal conversion has been done:

	  You have: 6 ohms
	  You want: siemens
		  reciprocal conversion
		  * 0.16666667
		  / 6

       Reciprocal conversion can be suppressed by using the '--strict' option.
       As usual, use the '--verbose' option to get more comprehensible output:

	  You have: tex
	  You want: typp
		  reciprocal conversion
		  1 / tex = 496.05465 typp
		  1 / tex = (1 / 0.0020159069) typp

	  You have: 20 mph
	  You want: sec/mile
		  reciprocal conversion
		  1 / 20 mph = 180 sec/mile
		  1 / 20 mph = (1 / 0.0055555556) sec/mile

       If you enter incompatible unit types, the 'units' program will print  a
       message	indicating that the units are not conformable and it will dis‐
       play the reduced form for each unit:

	  You have: ergs/hour
	  You want: fathoms kg^2 / day
	  conformability error
		  2.7777778e-11 kg m^2 / sec^3
		  2.1166667e-05 kg^2 m / sec

       If you only want to find the reduced form  or  definition  of  a  unit,
       simply press Enter at the 'You want:' prompt.  Here is an example:

	  You have: jansky
	  You want:
		  Definition: fluxunit = 1e-26 W/m^2 Hz = 1e-26 kg / s^2

       The  output  from  'units'  indicates  that the jansky is defined to be
       equal to a fluxunit which in turn is defined to be a  certain  combina‐
       tion  of watts, meters, and hertz.  The fully reduced (and in this case
       somewhat more cryptic) form appears on the far right.

       Some named units are  treated  as  dimensionless  in  some  situations.
       These  units  include  the  radian  and steradian.  These units will be
       treated as equal to 1 in units conversions.  Power is equal  to	torque
       times  angular  velocity.  This conversion can only be performed if the
       radian is dimensionless.

	  You have: (14 ft lbf) (12 radians/sec)
	  You want: watts
		  * 227.77742
		  / 0.0043902509

       Named dimensionless units are not treated  as  dimensionless  in  other
       contexts.    They   cannot   be	used  as  exponents  so  for  example,
       'meter^radian' is not allowed.

       If you want a list of options you can type  '?'	 at  the  'You	want:'
       prompt.	 The  program will display a list of named units that are con‐
       formable with the unit that you	entered  at  the  'You	have:'	prompt
       above.  Conformable unit combinations will not appear on this list.

       Typing  'help' at either prompt displays a short help message.  You can
       also type 'help' followed by a unit name.  This will invoke a pager  on
       the  units  data base at the point where that unit is defined.  You can
       read the definition and comments that may give more details or histori‐
       cal  information  about	the  unit.  (You can generally quit out of the
       page by pressing 'q'.)

       Typing 'search' text will display a list of  all  of  the  units  whose
       names  contain  text as a substring along with their definitions.  This
       may help in the case where you aren't sure of the right unit name.

USING UNITS NON-INTERACTIVELY
       The 'units' program can	perform  units	conversions  non-interactively
       from the command line.  To do this, type the command, type the original
       unit expression, and type the new units you want.  If a	units  expres‐
       sion  contains  non-alphanumeric characters, you may need to protect it
       from interpretation by the shell using single or double	quote  charac‐
       ters.

       If you type

	  units "2 liters" quarts

       then 'units' will print

	      * 2.1133764
	      / 0.47317647

       and then exit.  The output tells you that 2 liters is about 2.1 quarts,
       or alternatively that a quart is about 0.47 times 2 liters.

       If the conversion is  successful,  then	'units'  will  return  success
       (zero) to the calling environment.  If you enter  non-conformable units
       then 'units' will print a message giving the reduced form of each  unit
       and it will return failure (nonzero) to the calling environment.

       When  you  invoke 'units' with only one argument, it will print out the
       definition of the specified unit.  It will return failure if  the  unit
       is not defined and success if the unit is defined.

UNIT DEFINITIONS
       The  conversion	information  is  read  from  a units data file that is
       called	'definitions.units'   and   is	 usually   located   in    the
       '/usr/share/units'  directory.	If  you  invoke  'units' with the '-V'
       option, it will print the location of  this  file.   The  default  file
       includes  definitions  for all familiar units, abbreviations and metric
       prefixes.  It also includes many obscure or archaic units.

       Many constants of nature are defined, including these:

	  pi	      ratio of circumference to diameter
	  c	      speed of light
	  e	      charge on an electron
	  force       acceleration of gravity
	  mole	      Avogadro's number
	  water       pressure per unit height of water
	  Hg	      pressure per unit height of mercury
	  au	      astronomical unit
	  k	      Boltzman's constant
	  mu0	      permeability of vacuum
	  epsilon0    permittivity of vacuum
	  G	      Gravitational constant
	  mach	      speed of sound

       The standard data file includes atomic masses for all of  the  elements
       and numerous other constants.  Also included are the densities of vari‐
       ous ingredients used in baking so that '2  cups	flour_sifted'  can  be
       converted  to  'grams'.	 This  is not an exhaustive list.  Consult the
       units data file to see the complete list, or  to  see  the  definitions
       that are used.

       The  'pound'  is  a  unit of mass.  To get force, multiply by the force
       conversion unit 'force' or use the shorthand 'lbf'.  (Note that 'g'  is
       already	taken  as  the	standard abbreviation for the gram.)  The unit
       'ounce' is also a unit of mass.	The fluid  ounce  is  'fluidounce'  or
       'floz'.	British capacity units that differ from their US counterparts,
       such as the British Imperial gallon, are prefixed with 'br'.   Currency
       is prefixed with its country name: 'belgiumfranc', 'britainpound'.

       When  searching	for  a	unit,  if the specified string does not appear
       exactly as a unit name, then the 'units' program will try to  remove  a
       trailing 's', 'es'.  Next units will replace a trailing 'ies' with 'y'.
       If that fails, 'units' will check for a prefix.	The database  includes
       all  of the standard metric prefixes.  Only one prefix is permitted per
       unit, so 'micromicrofarad' will fail.   However,  prefixes  can	appear
       alone  with no unit following them, so 'micro*microfarad' will work, as
       will 'micro microfarad'.

       To find out which units and prefixes are available, read  the  standard
       units data file, which is extensively annotated.

   English Customary Units
       English	customary  units  differ in various ways in different regions.
       In Britain a complex system of volume measurements  featured  different
       gallons	for  different	materials such as a wine gallon and ale gallon
       that different by twenty percent.  This complexity was  swept  away  in
       1824 by a reform that created an entirely new gallon, the British Impe‐
       rial gallon defined as the volume occupied  by  ten  pounds  of	water.
       Meanwhile  in  the  USA	the gallon is derived from the 1707 Winchester
       wine gallon, which is 231 cubic inches.	These gallons differ by  about
       twenty  percent.   By default if 'units' runs in the 'en_GB' locale you
       will get the British volume measures.  If it runs in the 'en_US' locale
       you will get the US volume measures.  In other locales the default val‐
       ues are the US definitions.  If you wish to force different definitions
       then  set  the  environment  variable 'UNITS_ENGLISH' to either 'US' or
       'GB' to set the desired definitions independent of the locale.

       Before 1959, the value of a yard (and other units of measure defined in
       terms  of  it)  differed slightly among English-speaking countries.  In
       1959, Australia, Canada, New Zealand, the United  Kingdom,  the	United
       States,	and  South  Africa  adopted  the  Canadian  value  of 1 yard =
       0.9144 m (exactly), which was approximately halfway between the	values
       used  by  the  UK and the US; it had the additional advantage of making
       1 inch = 2.54 cm (exactly).  This new standard was termed the  Interna‐
       tional  Yard.  Australia, Canada, and the UK then defined all customary
       lengths in terms of the International Yard (Australia  did  not	define
       the  furlong or rod); because many US land surveys were in terms of the
       pre-1959 units, the US continued to define customary  surveyors'  units
       (furlong,  chain, rod, and link) in terms of the previous value for the
       foot, which was termed the US survey foot.  The US defined a US	survey
       mile  as 5280 US survey feet, and defined a statute mile as a US survey
       mile.  The US values for these units differ from the international val‐
       ues by about 2 ppm.

       The  'units' program uses the international values for these units; the
       US values can be obtained by using either the 'US' or the 'survey' pre‐
       fix.  In either case, the simple familiar relationships among the units
       are maintained, e.g., 1 'furlong' = 660 'ft', and 1 'USfurlong'	=  660
       'USft',	though	the metric equivalents differ slightly between the two
       cases.  The 'US' prefix or the 'survey' prefix  can  also  be  used  to
       obtain  the  US survey mile and the value of the US yard prior to 1959,
       e.g., 'USmile' or 'surveymile' (but not 'USsurveymile').  To get the US
       value of the statute mile, use either 'USstatutemile' or 'USmile'.

       Except for distances that extend over hundreds of miles (such as in the
       US State Plane Coordinate System), the differences  in  the  miles  are
       usually insignificant:

	  You have: 100 surveymile - 100 mile
	  You want: inch
		  * 12.672025
		  / 0.078913984

       The  pre-1959 UK values for these units can be obtained with the prefix
       'UK'.

       In the US, the acre is officially defined in terms  of  the  US	survey
       foot,  but  'units'  uses a definition based on the international foot.
       If you want the	official  US  acre  use  'USacre'  and	similarly  use
       'USacrefoot'  for the official US version of that unit.	The difference
       between these units is about 4 parts per million.

UNIT EXPRESSIONS
   Operators
       You can enter more complicated units by combining units with operations
       such  as  powers,  multiplication, division, addition, subtraction, and
       parentheses for grouping.  You can use the customary symbols for  these
       operators  when 'units' is invoked with its default options.  Addition‐
       ally, 'units' supports some extensions, including high priority	multi‐
       plication using a space, and a high priority numerical
	division operator ('|') that can simplify some expressions.

       Powers  of  units  can be specified using the '^' character as shown in
       the following example, or by simple concatenation of  a	unit  and  its
       exponent:  'cm3'  is equivalent to 'cm^3'; if the exponent is more than
       one digit, the '^' is required.	An exponent like '2^3^2' is  evaluated
       right  to  left	as  usual.   The  '^'  operator has the second highest
       precedence.  You can also use '**' as an exponent operator.

	  You have: cm^3
	  You want: gallons
		  * 0.00026417205
		  / 3785.4118

	  You have: arabicfoot * arabictradepound * force
	  You want: ft lbf
		  * 0.7296
		  / 1.370614

       You multiply units using a space or an  asterisk  ('*').   The  example
       above  shows both forms.  You can divide units using the slash ('/') or
       with 'per'.

	  You have: furlongs per fortnight
	  You want: m/s
		  * 0.00016630986
		  / 6012.8727

       When a unit includes a prefix, exponent operators apply to the combina‐
       tion,  so  'centimeter^3' gives cubic centimeters.  If you separate the
       prefix from the unit with any multiplication operator, such  as	'centi
       meter^3',  then	the prefix is treated as a separate unit, so the expo‐
       nent does not apply.  The second example would  be  a  hundredth  of  a
       cubic meter, not a centimeter.

       Multiplication  using  a  space	 has a higher precedence than division
       using a slash and is evaluated left to right; in effect, the first  '/'
       character  marks the beginning of the denominator of a unit expression.
       This makes it simple to enter a quotient  with  several	terms  in  the
       denominator:  'W  /  m^2  Hz'.	If you multiply with '*' then you must
       group the terms in the denominator with parentheses: 'W / (m^2 * Hz)'.

       The higher precedence of the space operator may not always be  advanta‐
       geous.  For example, 'm/s s/day' is equivalent to 'm / s s day' and has
       dimensions of length per time cubed.  Similarly, '1/2 meter' refers  to
       a  unit	of reciprocal length equivalent to 0.5/meter, perhaps not what
       you would intend if you entered that expression.  The '*'  operator  is
       convenient for multiplying a sequence of quotients.  With the '*' oper‐
       ator, the example above becomes 'm/s * s/day', which is	equivalent  to
       'm/day'.  Similarly, you could write '1/2 * meter' to get half a meter.
       Alternatively, parentheses can be used for grouping:  you  could  write
       '(1/2)  meter'  to  get half a meter.  See Complicated Unit Expressions
       for an illustration of the various options.

       The 'units' program supports another option  for  numerical  fractions.
       You can indicate division of numbers with the vertical bar ('|'), so if
       you wanted half a meter you could write '1|2 meter'.  This operator has
       the  highest precedence, so you can write the square root of two thirds
       '2|3^1|2'.  You cannot use the vertical bar  to	indicate  division  of
       non-numerical units (e.g., 'm|s' results in an error message).

	  You have: 1|2 inch
	  You want: cm
		  * 1.27
		  / 0.78740157

       You can use parentheses for grouping:

	  You have: (1/2) kg / (kg/meter)
	  You want: league
		  * 0.00010356166
		  / 9656.0833

   Sums and Differences of Units
       You  may  sometimes want to add values of different units that are out‐
       side the SI.  You may also wish to use 'units'  as  a  calculator  that
       keeps  track  of units.	Sums of conformable units are written with the
       '+' character, and differences with the '-' character.

	  You have: 2 hours + 23 minutes + 32 seconds
	  You want: seconds
		  * 8612
		  / 0.00011611705

	  You have: 12 ft + 3 in
	  You want: cm
		  * 373.38
		  / 0.0026782366

	  You have: 2 btu + 450 ft lbf
	  You want: btu
		  * 2.5782804
		  / 0.38785542

       The expressions that are added or subtracted must reduce  to  identical
       expressions in primitive units, or an error message will be displayed:

	  You have: 12 printerspoint - 4 heredium
						^
	  Illegal sum of non-conformable units

       As  usual,  the	precedence  for  '+' and '-' is lower than that of the
       other operators.  A fractional quantity such as 2 1/2 cups can be given
       as '(2+1|2) cups'; the parentheses are necessary because multiplication
       has higher precedence than addition.   If  you  omit  the  parentheses,
       'units'	attempts  to add '2' and '1|2 cups', and you get an error mes‐
       sage:

	  You have: 2+1|2 cups
			     ^
	  Illegal sum or difference of non-conformable units

       The expression could also be correctly written as '(2+1/2)  cups'.   If
       you  write  '2  1|2 cups' the space is interpreted as multiplication so
       the result is the same as '1 cup'.

       The  '+'  and  '-'  characters  sometimes  appears  in  exponents  like
       '3.43e+8'.  This leads to an ambiguity in an expression like '3e+2 yC'.
       The unit 'e' is a small unit of charge, so  this  can  be  regarded  as
       equivalent  to  '(3e+2)	yC'  or  '(3  e)+(2  yC)'.   This ambiguity is
       resolved by always interpreting '+' and '-' as part of an  exponent  if
       possible.

   Numbers as Units
       For 'units', numbers are just another kind of unit.  They can appear as
       many times as you like and in any order	in  a  unit  expression.   For
       example,  to  find the volume of a box that is 2 ft by 3 ft by 12 ft in
       steres, you could do the following:

	  You have: 2 ft 3 ft 12 ft
	  You want: stere
		  * 2.038813
		  / 0.49048148

	  You have: $ 5 / yard
	  You want: cents / inch
		  * 13.888889
		  / 0.072

       And the second example shows how the dollar sign in the	units  conver‐
       sion  can  precede  the	five.  Be careful: 'units' will interpret '$5'
       with no space as equivalent to 'dollar^5'.

   Built-in Functions
       Several built-in functions are provided:  'sin',  'cos',  'tan',  'ln',
       'log', 'log2', 'exp', 'acos', 'atan' and 'asin'.  The 'sin', 'cos', and
       'tan' functions require either a dimensionless argument or an  argument
       with dimensions of angle.

	  You have: sin(30 degrees)
	  You want:
		  Definition: 0.5

	  You have: sin(pi/2)
	  You want:
		  Definition: 1

	  You have: sin(3 kg)
			    ^
	  Unit not dimensionless

       The  other  functions on the list require dimensionless arguments.  The
       inverse trigonometric functions return  arguments  with	dimensions  of
       angle.

       If  you	wish  to  take	roots  of  units,  you	may  use the 'sqrt' or
       'cuberoot' functions.  These functions require that the	argument  have
       the  appropriate root.  You can obtain higher roots by using fractional
       exponents:

	  You have: sqrt(acre)
	  You want: feet
		  * 208.71074
		  / 0.0047913202

	  You have: (400 W/m^2 / stefanboltzmann)^(1/4)
	  You have:
		  Definition: 289.80882 K

	  You have: cuberoot(hectare)
				    ^
	  Unit not a root

   Complicated Unit Expressions
       The 'units' program is especially  helpful  in  ensuring  accuracy  and
       dimensional  consistency when converting lengthy unit expressions.  For
       example, one form of the Darcy-Weisbach fluid-flow equation is

	    Delta P = (8 / pi)^2 (rho fLQ^2) / d^5,

       where Delta P is the pressure drop, rho is the mass density, f  is  the
       (dimensionless)	friction factor, L is the length of the pipe, Q is the
       volumetric flow rate, and d is the pipe diameter.  It might be  desired
       to have the equation in the form

	    Delta P = A1 rho fLQ^2 / d^5

       that  accepted  the  user's normal units; for typical units used in the
       US, the required conversion could be something like

	  You have: (8/pi^2)(lbm/ft^3)ft(ft^3/s)^2(1/in^5)
	  You want: psi
		  * 43.533969
		  / 0.022970568

       The parentheses allow individual terms in the expression to be  entered
       naturally,  as they might be read from the formula.  Alternatively, the
       multiplication could be done with the '*' rather  than  a  space;  then
       parentheses are needed only around 'ft^3/s' because of its exponent:

	  You have: 8/pi^2 * lbm/ft^3 * ft * (ft^3/s)^2 /in^5
	  You want: psi
		  * 43.533969
		  / 0.022970568

       Without	parentheses, and using spaces for multiplication, the previous
       conversion would need to be entered as

	  You have: 8 lb ft ft^3 ft^3 / pi^2 ft^3 s^2 in^5
	  You want: psi
		  * 43.533969
		  / 0.022970568

   Backwards Compatibility:
       '*' and '-' The	original  'units'  assigned  multiplication  a	higher
       precedence  than division using the slash.  This differs from the usual
       precedence rules, which give multiplication and division  equal	prece‐
       dence, and can be confusing for people who think of units as a calcula‐
       tor.

       The star operator ('*')	included  in  this  'units'  program  has,  by
       default,  the  same precedence as division, and hence follows the usual
       precedence rules.  For backwards compatibility you can  invoke  'units'
       with  the  '--oldstar'  option.	 Then '*' has a higher precedence than
       division, and the same precedence as multiplication using the space.

       Historically, the hyphen ('-') has been used in technical  publications
       to indicate products of units, and the original 'units' program treated
       it as a multiplication  operator.   Because  'units'  provides  several
       other  ways  to	obtain unit products, and because '-' is a subtraction
       operator in general algebraic expressions, 'units'  treats  the	binary
       '-'  as a subtraction operator by default.  For backwards compatibility
       use the '--product' option, which causes 'units' to  treat  the	binary
       '-' operator as a product operator.  When '-' is a multiplication oper‐
       ator it has the same precedence as multiplication with a space,	giving
       it a higher precedence than division.

       When  '-'  is used as a unary operator it negates its operand.  Regard‐
       less of the 'units' options, if '-' appears after '(' or after '+' then
       it  will  act  as  a  negation  operator.  So you can always compute 20
       degrees minus 12 minutes by entering '20 degrees +  -12	arcmin'.   You
       must use this construction when you define new units because you cannot
       know what options will be in force when your definition is processed.

NONLINEAR UNIT CONVERSIONS
       Nonlinear units are represented using functional notation.   They  make
       possible nonlinear unit conversions such as temperature.

   Temperature Conversions
       Conversions  between temperatures are different from linear conversions
       between temperature increments—see the  example	below.	 The  absolute
       temperature  conversions are handled by units starting with 'temp', and
       you must use functional notation.   The	temperature-increment  conver‐
       sions  are done using units starting with 'deg' and they do not require
       functional notation.

	  You have: tempF(45)
	  You want: tempC
		  7.2222222

	  You have: 45 degF
	  You want: degC
		  * 25
		  / 0.04

       Think of 'tempF(x)' not as a function but as a notation that  indicates
       that  x should have units of 'tempF' attached to it.  See Defining Non‐
       linear Units.  The first conversion  shows  that  if  it's  45  degrees
       Fahrenheit  outside,  it's  7.2 degrees Celsius.  The second conversion
       indicates that a change of  45  degrees	Fahrenheit  corresponds  to  a
       change  of  25  degrees	Celsius.  The conversion from 'tempF(x)' is to
       absolute temperature, so that

	  You have: tempF(45)
	  You want: degR
		  * 504.67
		  / 0.0019814929

       gives the same result as

	  You have: tempF(45)
	  You want: tempR
		  * 504.67
		  / 0.0019814929

       But if you convert 'tempF(x)' to 'degC', the  output  is  probably  not
       what you expect:

	  You have: tempF(45)
	  You want: degC
		  * 280.37222
		  / 0.0035666871

       The  result  is the temperature in K, because 'degC' is defined as 'K',
       the Kelvin. For consistent results, use the 'tempX' units when convert‐
       ing to a temperature rather than converting a temperature increment.

   Other Nonlinear Units
       Some  other  examples  of  nonlinear  units are numerous different ring
       sizes and wire gauges, the grit sizes used for abrasives,  the  decibel
       scale,  shoe  size,  scales for the density of sugar (e.g. baume).  The
       standard data file also supplies units for computing the area of a cir‐
       cle  and  the volume of a sphere.  See the standard units data file for
       more details.  Wire gauges with multiple  zeroes  are  signified  using
       negative  numbers where two zeroes is '-1'.  Alternatively, you can use
       the synonyms 'g00', 'g000', and so on that are defined in the  standard
       units data file.

	  You have: wiregauge(11)
	  You want: inches
		  * 0.090742002
		  / 11.020255

	  You have: brwiregauge(g00)
	  You want: inches
		  * 0.348
		  / 2.8735632

	  You have: 1 mm
	  You want: wiregauge
		  18.201919

	  You have: grit_P(600)
	  You want: grit_ansicoated
		  342.76923

       The  last  example shows the conversion from P graded sand paper, which
       is the European standard and may be marked ``P600'' on the back, to the
       USA standard.

       You  can  compute  the  area  of  a  circle  using  the nonlinear unit,
       'circlearea'.  You can also do this  using  the	circularinch  or  cir‐
       cleinch.  The next example shows two ways to compute the area of a cir‐
       cle with a five inch radius and one way to  compute  the  volume  of  a
       sphere with a radius of one meter.

	  You have: circlearea(5 in)
	  You want: in2
		  * 78.539816
		  / 0.012732395

	  You have: 10^2 circleinch
	  You want: in2
		  * 78.539816
		  / 0.012732395

	  You have: spherevol(meter)
	  You want: ft3
		  * 147.92573
		  / 0.0067601492

UNIT LISTS: CONVERSION TO SUMS OF UNITS
       Outside	of  the SI, it is sometimes desirable to convert a single unit
       to a sum of units—for example, feet to feet plus inches.   The  conver‐
       sion from sums of units was described in Sums and Differences of Units,
       and is a simple matter of adding the units with the '+' sign:

	  You have: 12 ft + 3 in + 3|8 in
	  You want: ft
		  * 12.28125
		  / 0.081424936

       Although you can similarly write a sum of  units  to  convert  to,  the
       result  will  not be the conversion to the units in the sum, but rather
       the conversion to the particular sum that you have entered:

	  You have: 12.28125 ft
	  You want: ft + in + 1|8 in
		  * 11.228571
		  / 0.089058524

       The unit expression given at the 'You want:' prompt  is	equivalent  to
       asking  for conversion to multiples of '1 ft + 1 in + 1|8 in', which is
       1.09375 ft, so the conversion in the previous example is equivalent to

	  You have: 12.28125 ft
	  You want: 1.09375 ft
		  * 11.228571
		  / 0.089058524

       In converting to a sum of units like miles, feet and inches, you  typi‐
       cally  want  the largest integral value for the first unit, followed by
       the largest integral value for the next, and the remainder converted to
       the  last unit.	You can do this conversion easily with 'units' using a
       special syntax for lists of units.  You must list the desired units  in
       order  from largest to smallest, separated by the semicolon (';') char‐
       acter:

	  You have: 12.28125 ft
	  You want: ft;in;1|8 in
		  12 ft + 3 in + 3|8 in

       The conversion always gives integer coefficients on the	units  in  the
       list, except possibly the last unit when the conversion is not exact:

	  You have: 12.28126 ft
	  You want: ft;in;1|8 in
		  12 ft + 3 in + 3.00096 * 1|8 in

       The order in which you list the units is important:

	  You have: 3 kg
	  You want: oz;lb
		  105 oz + 0.051367866 lb

	  You have: 3 kg
	  You want: lb;oz
		  6 lb + 9.8218858 oz

       Listing ounces before pounds produces a technically correct result, but
       not a very useful one.  You must list the units in descending order  of
       size in order to get the most useful result.

       Ending  a  unit	list  with  the  separator  ';' has the same effect as
       repeating the last unit on the list, so 'ft;in;1|8 in;'	is  equivalent
       to 'ft;in;1|8 in;1|8 in'.  With the example above, this gives

	  You have: 12.28126 ft
	  You want: ft;in;1|8 in;
		  12 ft + 3 in + 3|8 in + 0.00096 * 1|8 in

       in  effect  separating  the integer and fractional parts of the coeffi‐
       cient for the last unit.  If you instead prefer to round the last coef‐
       ficient to an integer you can do this with the '--round' ('-r') option.
       With the previous example, the result is

	  You have: 12.28126 ft
	  You want: ft;in;1|8 in
		  12 ft + 3 in + 3|8 in (rounded down to nearest 1|8 in)

       When you use the '-r' option, repeating the last unit on the  list  has
       no  effect  (e.g.,  'ft;in;1|8  in;1|8  in' is equivalent to 'ft;in;1|8
       in'), and hence neither does ending a list with a ';'.  With  a	single
       unit and the '-r' option, a terminal ';' does have an effect: it causes
       'units' to treat the single unit as a list and produce a rounded  value
       for  the  single  unit.	 Without the extra ';', the '-r' option has no
       effect on single unit conversions.  This example shows the output using
       the '-r' option:

	  You have: 12.28126 ft
	  You want: in
		  * 147.37512
		  / 0.0067854058

	  You have: 12.28126 ft
	  You want: in;
		  147 in (rounded down to nearest in)

       Each  unit  that appears in the list must be conformable with the first
       unit on the list, and of course the listed units must also be  conform‐
       able with the You have unit that you enter.

	  You have: meter
	  You want: ft;kg
		       ^
	  conformability error
		  ft = 0.3048 m
		  kg = 1 kg

	  You have: meter
	  You want: lb;oz
	  conformability error
		  1 m
		  0.45359237 kg

       In  the	first  case,  'units'  reports	the disagreement between units
       appearing on the list.  In the second case, 'units'  reports  disagree‐
       ment  between  the  unit  you entered and the desired conversion.  This
       conformability error is based on the first unit on the unit list.

       Other common candidates for conversion to sums of units are angles  and
       time:

	  You have: 23.437754 deg
	  You want; deg;arcmin;arcsec
	      23 deg + 26 arcmin + 15.9144 arcsec

	      You have: 7.2319 hr
	      You want: hr;min;sec
		  7 hr + 13 min + 54.84 sec

       In  North America, recipes for cooking typically measure ingredients by
       volume, and use units that are not always convenient multiples of  each
       other.	Suppose  that  you  have a recipe for 6 and you wish to make a
       portion for 1.  If the recipe calls for 2 1/2 cups  of  an  ingredient,
       you  might  wish to know the measurements in terms of measuring devices
       you have available, you could use 'units' and enter

	  You have: (2+1|2) cup / 6
	  You want: cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp
		  1|3 cup + 1 tbsp + 1 tsp

       By default, if a unit in a list begins with fraction of	the  form  1|x
       and  its multiplier is an integer, the fraction is given as the product
       of the multiplier and the numerator; for example,

	  You have: 12.28125 ft
	  You want: ft;in;1|8 in;
		  12 ft + 3 in + 3|8 in

       In many cases, such as the example above, this is what is  wanted,  but
       sometimes  it  is  not.	For example, a cooking recipe for 6 might call
       for 5 1/4 cup of an ingredient, but you want a portion for 2, and  your
       1-cup measure is not available; you might try

	  You have: (5+1|4) cup / 3
	  You want: 1|2 cup;1|3 cup;1|4 cup
		  3|2 cup + 1|4 cup

       This  result might be fine for a baker who has a 1 1/2-cup measure (and
       recognizes the equivalence), but it may not be  as  useful  to  someone
       with  more limited set of measures, who does want to do additional cal‐
       culations, and only wants to know ``How many 1/2-cup measures to I need
       to  add?''   After  all,  that's  what  was  actually  asked.  With the
       '--show-factor' option, the factor will not be combined	with  a  unity
       numerator, so that you get

	  You have: (5+1|4) cup / 3
	  You want: 1|2 cup;1|3 cup;1|4 cup
		  3 * 1|2 cup + 1|4 cup

       A user-specified fractional unit with a numerator other than 1 is never
       overridden, however—if a unit  list  specifies  '3|4  cup;1|2  cup',  a
       result  equivalent  to 1 1/2 cups will always be shown as '2 * 3|4 cup'
       whether or not the '--show-factor' option is given.

       Some applications for unit lists may be less obvious.  Suppose that you
       have  a postal scale and wish to ensure that it's accurate at 1 oz, but
       have only metric calibration weights.  You might try

	  You have: 1 oz
	  You want: 100 g;50 g; 20 g;10 g;5 g;2 g;1 g;
		  20 g + 5 g + 2 g + 1 g + 0.34952312 * 1 g

       You might then place one each of the 20 g, 5 g, 2 g, and 1 g weights on
       the scale and hope that it indicates close to

	  You have: 20 g + 5 g + 2 g + 1 g
	  You want: oz;
		  0.98767093 oz

       Appending ';' to 'oz' forces a one-line display that includes the unit;
       here the integer part of the result is zero, so it is not displayed.

       A unit list such as

	  cup;1|2 cup;1|3 cup;1|4 cup;tbsp;tsp;1|2 tsp;1|4 tsp

       can be tedious to enter.  The 'units' program provides shorthand  names
       for some common combinations:

	  hms	      hours, minutes, seconds
	  dms	      angle: degrees, minutes, seconds
	  time	      years, days, hours, minutes and seconds
	  usvol       US cooking volume: cups and smaller

       Using  these shorthands, or unit list aliases, you can do the following
       conversions:

	  You have: anomalisticyear
	  You want: time
		  1 year + 25 min + 3.4653216 sec
	  You have: 1|6 cup
	  You want: usvol
		  2 tbsp + 2 tsp

       You cannot combine a unit list alias with other units: it  must	appear
       alone at the 'You want:' prompt.

       You  can  display the definition of a unit list alias by entering it at
       the 'You have:' prompt:

	  You have: dms
		  Definition: unit list, deg;arcmin;arcsec

       When you specify compact output with '--compact', '--terse' or '-t' and
       perform conversion to a unit list, 'units' lists the conversion factors
       for each unit in the list, separated by semicolons.

	  You have: year
	  You want: day;min;sec
	  365;348;45.974678

       Unlike the case of regular output, zeros are included  in  this	output
       list:

	  You have: liter
	  You want: cup;1|2 cup;1|4 cup;tbsp
	  4;0;0;3.6280454

INVOKING UNITS
       You invoke 'units' like this:

	  units [options] [from-unit [to-unit]]

       If the from-unit and to-unit are omitted, the program will use interac‐
       tive prompts to determine which conversions to perform.	 See  Interac‐
       tive  Use.  If both from-unit and to-unit are given, 'units' will print
       the result of that single conversion and then exit.  If only  from-unit
       appears	on  the  command  line, 'units' will display the definition of
       that unit and exit.  Units specified on the command line may need to be
       quoted to protect them from shell interpretation and to group them into
       two arguments.  See Command Line Use.

       The default behavior of 'units' can be changed by various options given
       on the command line.  In most cases, the options may be given in either
       short form (a single '-' followed by a single character) or  long  form
       ('--'  followed	by  a  word  or  hyphen-separated  words).  Short-form
       options are cryptic but require less typing; long-form options  require
       more  typing  but  are more explanatory and may be more mnemonic.  With
       long-form options you need only enter sufficient characters to uniquely
       identify the option to the program.  For example, '--out %f' works, but
       '--o %f' fails because 'units' has other long  options  beginning  with
       'o'.   However,	'--q'  works because '--quiet' is the only long option
       beginning with 'q'.

       Some options require arguments to specify a  value  (e.g.,  '-d 12'  or
       '--digits 12').	 Short-form  options that do not take arguments may be
       concatenated (e.g., '-erS'  is  equivalent  to  '-e -r -S');  the  last
       option  in  such  a  list  may  be  one	that  takes an argument (e.g.,
       '-ed 12').  With short-form options, the space between  an  option  and
       its  argument  is  optional  (e.g.,  '-d12'  is equivalent to '-d 12').
       Long-form options may not be concatenated,  and	the  space  between  a
       long-form  option  and  its argument is required.  Short-form and long-
       form options may be intermixed on the command  line.   Options  may  be
       given  in  any  order,  but when incompatible options (e.g., '--output-
       format' and '--exponential') are given in combination, behavior is con‐
       trolled	by  the  last  option  given.  For example, '-o%.12f -e' gives
       exponential format with the default eight significant digits).

       The following options are available:

       -c, --check
	      Check that all units and prefixes defined in the units data file
	      reduce  to primitive units.  Print a list of all units that can‐
	      not be reduced.  Also display some other diagnostics about  sus‐
	      picious  definitions  in	the units data file.  Only definitions
	      active in the current locale are checked.  You should always run
	      'units' with this option after modifying a units data file.

       --check-verbose, --verbose-check
	      Like  the  '--check'  option, this option prints a list of units
	      that cannot be reduced.  But to help find unit  definitions that
	      cause endless loops, it lists the units as they are checked.  If
	      'units' hangs, then the last unit to be printed has a bad  defi‐
	      nition.	Only  definitions  active  in  the  current locale are
	      checked.

       -d ndigits, --digits ndigits
	      Set the number of significant digits in the output to the  value
	      specified  (which  must  be  greater  than  zero).  For example,
	      '-d 12' sets the number of significant digits to 12.  With expo‐
	      nential  output  'units'	displays  one digit to the left of the
	      decimal point and eleven digits to  the  right  of  the  decimal
	      point.   On most systems, the maximum number of internally mean‐
	      ingful digits is 15; if you specify a greater number  than  your
	      system's	maximum, 'units' will print a warning and set the num‐
	      ber to the largest meaningful value.  To directly set the  maxi‐
	      mum  value,  give  an  argument  of  'max' (e.g., '-d max').  Be
	      aware, of course, that ``significant'' here refers only  to  the
	      display  of numbers; if results depend on physical constants not
	      known to this precision, the physically meaningful precision may
	      be  less	than that shown.  The '--digits' option conflicts with
	      the '--output-format' option.

       -e, --exponential
	      Set the numeric output format to exponential  (i.e.,  scientific
	      notation),  like	that  used  in	the Unix 'units' program.  The
	      default precision is eight significant digits (seven  digits  to
	      the  right  of  the decimal point); this can be changed with the
	      '--digits' option.  The '--exponential'  option  conflicts  with
	      the '--output-format' option.

       -o format, --output-format format
	      This  option  affords  complete  control over the numeric output
	      format using the specified format. The format is a single float‐
	      ing  point  numeric  format for the 'printf()' function in the C
	      programming language.  All compilers support  the  format  types
	      'g'  and 'G' to specify significant digits, 'e' and 'E' for sci‐
	      entific notation, and 'f' for fixed-point decimal.  The ISO  C99
	      standard introduced the 'F' type for fixed-point decimal and the
	      'a' and 'A' types for hexadecimal floating  point;  these  types
	      are  allowed with compilers that support them.  The default for‐
	      mat  is  '%.8g';	for  greater  precision,  you  could   specify
	      '-o %.15g'.  See Numeric Output Format and the documentation for
	      'printf()' for more detailed descriptions of the format specifi‐
	      cation.	The '--output-format' option affords the greatest con‐
	      trol of the output appearance, but requires at least rudimentary
	      knowledge of the 'printf()' format syntax.  If you don't want to
	      bother with the 'printf()' syntax, you can specify greater  pre‐
	      cision more simply with the '--digits' option or select exponen‐
	      tial format with '--exponential'.  The '--output-format'	option
	      is incompatible with the '--exponential' and '--digits' options.

       -f filename, --file filename
	      Instruct	'units'  to  load  the units file 'filename'.  You can
	      specify up to 25 units files on the command line.  When you  use
	      this  option,  'units'  will load only the files you list on the
	      command line; it will not load the standard file	or  your  per‐
	      sonal  units  file unless you explicitly list them.  If filename
	      is the empty string ('-f ""'), the default units file  (or  that
	      specified by 'UNITSFILE') will be loaded in addition to any oth‐
	      ers specified with '-f'.

       -h, --help
	      Print out a summary of the options for 'units'.

       -m, --minus
	      Causes '-' to be interpreted as a subtraction operator.  This is
	      the default behavior.

       -p, --product
	      Causes  '-'  to be interpreted as a multiplication operator when
	      it has two operands.  It will act as a negation operator when it
	      has  only  one  operand: '(-3)'.	By default '-' is treated as a
	      subtraction operator.

       --oldstar
	      Causes '*' to have the old-style	precedence,  higher  than  the
	      precedence of division so that '1/2*3' will equal '1/6'.

       --newstar
	      Forces '*' to have the new (default) precedence that follows the
	      usual rules of algebra: the precedence of '*' is the same as the
	      precedence of '/', so that '1/2*3' will equal '3/2'.

       --compact
	      Give  compact output featuring only the conversion factor.  This
	      turns off the '--verbose' option.

       -q, --quiet, --silent
	      Suppress prompting of the user for units and the display of sta‐
	      tistics about the number of units loaded.

       -n, --nolists
	      Disable conversion to unit lists.

       -r, --round
	      When  converting to a combination of units given by a unit list,
	      round the value of the last unit in  the	list  to  the  nearest
	      integer.

       -S, --show-factor
	      When  converting	to a combination of units specified in a list,
	      always show a non-unity factor before a unit that begins with  a
	      fraction with a unity denominator.  By default, if the unit in a
	      list begins with fraction of the form 1|x and its multiplier  is
	      an integer other than 1, the fraction is given as the product of
	      the multiplier and the numerator (e.g., '3|8 in' rather than  '3
	      *  1|8  in').   In  some	cases, this is not what is wanted; for
	      example, the results for a cooking recipe might show  '3	*  1|2
	      cup'  as	'3|2  cup'.  With the '--show-factor' option, a result
	      equivalent to 1.5 cups will display as '3 * 1|2 cup' rather than
	      '3|2  cup'.   A  user-specified fractional unit with a numerator
	      other than 1 is never overridden, however—if a unit list	speci‐
	      fies  '3|4  cup;1|2 cup', a result equivalent to 1 1/2 cups will
	      always be shown as '2 * 3|4 cup' whether	or  not  the  '--show-
	      factor' option is given.

       -s, --strict
	      Suppress	conversion  of	units  to their reciprocal units.  For
	      example, 'units' will normally convert hertz to seconds  because
	      these  units  are  reciprocals of each other.  The strict option
	      requires that units be strictly conformable to perform a conver‐
	      sion,  and will give an error if you attempt to convert hertz to
	      seconds.

       -1, --one-line
	      Give only one line of output (the forward conversion).   Do  not
	      print  the  reverse  conversion.	 If a reciprocal conversion is
	      performed then 'units' will still print the ``reciprocal conver‐
	      sion'' line.

       -t, --terse
	      Give  terse  output  when  converting units.  This option can be
	      used when calling 'units' from another program so that the  out‐
	      put  is  easy  to parse.	This option has the combined effect of
	      these options: '--strict' '--quiet' '--one-line' '--compact'.

       -v, --verbose
	      Give slightly more verbose output when converting  units.   When
	      combined	with  the  '-c'  option  this gives the same effect as
	      '--check-verbose'.

       -V, --version
	      Print  program  version  number,	tell  whether  the  'readline'
	      library  has been included, and give the location of the default
	      units data file.

       -l locale, --locale locale
	      Force a specified locale such as 'en_GB' to get British  defini‐
	      tions  by  default.   This  overrides the locale determined from
	      system settings or environment  variables.   See	Locale	for  a
	      description of locale format.

ADDING YOUR OWN DEFINITIONS
   Units Data Files
       The  units  and	prefixes  that	'units' can convert are defined in the
       units  data   file,   typically	 '/usr/share/units/definitions.units'.
       Although  you can extend or modify this data file if you have appropri‐
       ate user privileges, it's usually better to put extensions in  separate
       files  so  that	the  definitions  will	be  preserved  when you update
       'units'.

       You can include additional data files in the units database  using  the
       '!include' command in the standard units data file. For example

	  !include    /usr/local/share/units/local.units

       might be appropriate for a site-wide supplemental data file.  The loca‐
       tion of the '!include' statement in the standard  units	data  file  is
       important;  later  definitions replace earlier ones, so any definitions
       in an included file will override  definitions  before  the  '!include'
       statement  in the standard units data file.  With normal invocation, no
       warning is given about redefinitions; to ensure that you don't have  an
       unintended  redefinition,  run  'units -c'  after making changes to any
       units data file.

       If you want to add your own units in addition to or in place  of  stan‐
       dard  or  site-wide supplemental units data files, you can include them
       in the '.units' file in your home directory.  If this file exists it is
       read  after  the  standard  units data file, so that any definitions in
       this file will replace definitions of the same units  in  the  standard
       data  file or in files included from the standard data file.  This file
       will not be read if any units files are specified on the command  line.
       (Under Windows the personal units file is named 'unitdef.units'.)

       The  'units'  program first tries to determine your home directory from
       the 'HOME' environment variable.  On systems running Microsoft Windows,
       if  'HOME' does not exist, 'units' attempts to find your home directory
       from 'HOMEDRIVE' and 'HOMEPATH'.  Running 'units -V' will  display  the
       location and name of your personal units file.

       You can specify an arbitrary file as your personal units data file with
       the 'MYUNITSFILE' environment variable; if this	variable  exists,  its
       value is used without searching your home directory.

   Defining New Units and Prefixes
       A  unit is specified on a single line by giving its name and an equiva‐
       lence.  Comments start with a '#' character, which can appear  anywhere
       in  a line.  The backslash character ('\') acts as a continuation char‐
       acter if it appears as the last character on a line, making it possible
       to spread definitions out over several lines if desired.  A file can be
       included by giving the command '!include' followed by the file's  name.
       The  '!'   must	be  the first character on the line.  The file will be
       sought in the same directory as the parent file unless you give a  full
       path.   The  name of the file to be included cannot contain the comment
       character '#'.

       Unit names must not contain any of the operator	characters  '+',  '-',
       '*',  '/',  '|', '^', ';', '~', the comment character '#', or parenthe‐
       ses.  They cannot begin or end with an underscore ('_'), a comma  (',')
       or  a  decimal  point  ('.').   The figure dash (U+2012), typographical
       minus (`-'; U+2212), and en dash (`-'; U+2013)  are  converted  to  the
       operator  '-',  so  none  of these characters can appear in unit names.
       Names cannot begin with a digit, and if a name ends in  a  digit  other
       than  zero,  the  digit	must be preceded by a string beginning with an
       underscore, and afterwards consisting only of digits,  decimal  points,
       or  commas.   For  example,  'foo_2', 'foo_2,1', or 'foo_3.14' would be
       valid names but 'foo2' or 'foo_a2' would be invalid.  You could	define
       nitrous oxide as

	  N2O	  nitrogen 2  + oxygen

       but would need to define nitrogen dioxide as

	  NO_2	  nitrogen + oxygen 2

       Be careful to define new units in terms of old ones so that a reduction
       leads to the primitive units, which are marked  with  '!'   characters.
       Dimensionless  units are indicated by using the string '!dimensionless'
       for the unit definition.

       When adding new units, be sure to use the '-c' option to check that the
       new  units  reduce properly.  If you create a loop in the units defini‐
       tions, then 'units' will hang when invoked with the '-c'  option.   You
       will  need  to  use the '--check-verbose' option, which prints out each
       unit as it is checked.  The program will still hang, but the last  unit
       printed will be the unit that caused the infinite loop.

       If  you	define	any units that contain '+' characters, carefully check
       them because the '-c' option will not catch non-conformable  sums.   Be
       careful with the '-' operator as well.  When used as a binary operator,
       the '-' character can perform addition or multiplication  depending  on
       the  options used to invoke 'units'.  To ensure consistent behavior use
       '-' only as a unary negation operator when writing  units  definitions.
       To  multiply two units leave a space or use the '*' operator with care,
       recalling that it has two possible precedence values  and  may  require
       parentheses  to	ensure consistent behavior.  To compute the difference
       of 'foo' and 'bar' write 'foo+(-bar)' or even 'foo+-bar'.

       Here is an example of a short data file that defines some basic units:

	  m	  !		  # The meter is a primitive unit
	  sec	  !		  # The second is a primitive unit
	  rad	  !dimensionless  # A dimensionless primitive unit
	  micro-  1e-6		  # Define a prefix
	  minute  60 sec	  # A minute is 60 seconds
	  hour	  60 min	  # An hour is 60 minutes
	  inch	  0.0254 m	  # Inch defined in terms of meters
	  ft	  12 inches	  # The foot defined in terms of inches
	  mile	  5280 ft	  # And the mile

       A unit that ends with a '-' character is a prefix.  If a prefix defini‐
       tion  contains any '/' characters, be sure they are protected by paren‐
       theses.	If you define 'half- 1/2' then 'halfmeter' would be equivalent
       to '1 / (2 meter)'.

   Defining Nonlinear Units
       Some  unit conversions of interest are nonlinear; for example, tempera‐
       ture conversions between the Fahrenheit and Celsius  scales  cannot  be
       done by simply multiplying by conversion factors.

       When  you  give a linear unit definition such as 'inch 2.54 cm' you are
       providing information that 'units' uses to  convert  values  in	inches
       into  primitive units of meters.  For nonlinear units, you give a func‐
       tional definition that provides the same information.

       Nonlinear units are represented using a	functional  notation.	It  is
       best  to  regard  this  notation not as a function call but as a way of
       adding units to a number, much the same way that writing a linear  unit
       name  after  a number adds units to that number.  Internally, nonlinear
       units are defined by a pair of functions that convert to and from  lin‐
       ear units in the data file, so that an eventual conversion to primitive
       units is possible.

       Here is an example nonlinear unit definition:

	  tempF(x) units=[1;K] (x+(-32)) degF + stdtemp ; \
			       (tempF+(-stdtemp))/degF + 32

       A nonlinear unit definition comprises a unit name,  a  dummy  parameter
       name,  two  functions, and two corresponding units.  The functions tell
       'units' how to convert to and from the new unit.  In order  to  produce
       valid  results,	the arguments of these functions need to have the cor‐
       rect dimensions.  To facilitate	error  checking,  you  may  optionally
       indicate units for these arguments.

       The  definition begins with the unit name followed immediately (with no
       spaces) by a '(' character.  In parentheses is the name of the  parame‐
       ter.   Next  is	an optional specification of the units required by the
       functions in this definition.  In the example above, the 'tempF'  func‐
       tion  requires an input argument conformable with '1'.  For normal non‐
       linear units definitions the forward function will always take a dimen‐
       sionless  argument.   The  inverse  function requires an input argument
       conformable with 'K'.  In general the inverse function will need  units
       that  match  the quantity measured by your nonlinear unit.  The purpose
       of the expression in brackets to enable 'units' to perform error check‐
       ing on function arguments, and also to assign units to range and domain
       specifications, which are described later.

       Next the function  definitions  appear.	 In  the  example  above,  the
       'tempF' function is defined by

	  tempF(x) = (x+(-32)) degF + stdtemp

       This  gives  a  rule  for converting 'x' in the units 'tempF' to linear
       units of absolute temperature, which makes it possible to convert  from
       tempF to other units.

       In  order  to  make conversions to Fahrenheit possible, you must give a
       rule for the inverse conversions. The inverse will  be  'x(tempF)'  and
       its  definition	appears  after	a  ';' character.  In our example, the
       inverse is

	  x(tempF) = (tempF+(-stdtemp))/degF + 32

       This inverse definition takes an absolute temperature as  its  argument
       and  converts  it  to  the  Fahrenheit temperature.  The inverse can be
       omitted by leaving out the ';' character, but then conversions  to  the
       unit  will be impossible.  If the inverse is omitted then the '--check'
       option will display a warning.  It is up to you to calculate and  enter
       the  correct  inverse  function	to  obtain  proper  conversions.   The
       '--check' option tests the inverse at one point and prints an error  if
       it is not valid there, but this is not a guarantee that your inverse is
       correct.

       If you wish to make synonyms for nonlinear units,  you  still  need  to
       define  both  the forward and inverse functions.  Inverse functions can
       be obtained using the '~' operator.  So to create a synonym for 'tempF'
       you could write

	  fahrenheit(x) units=[1;K] tempF(x); ~tempF(fahrenheit)

       You  may  define  a function whose range and domain do not cover all of
       the real numbers.  In this case 'units' can handle errors better if you
       specify	an  appropriate  range	and domain.  You specify the range and
       domain as shown below.

	  baume(d) units=[1;g/cm^3] domain=[0,130.5] range=[1,10] \
		   (145/(145-d)) g/cm^3 ; (baume+-g/cm^3) 145 / baume

       In this example the domain is specified after the  'domain='  with  the
       endpoints  given  in brackets.  One of the end points can be omitted to
       get an interval that goes to infinity.  So the range could be specified
       as  nonnegative by writing 'range=[0,]'.  Both the range and domain are
       optional and can appear independently and in any order along  with  the
       'units' specification.  The values in the range and domain are attached
       to the units given in the 'units' specification.  If you don't  specify
       the  units then the parameter inputs are reduced to primitive units for
       the numeric comparison to the values you give in the range  or  domain.
       In  this  case you should only use 'range' or 'domain' if the endpoints
       are zero and infinity.

       Specifying the range and domain allows 'units' to perform better  error
       checking and give more helpful error messages when you invoke nonlinear
       units conversions outside of their bounds.  It also  enables  the  '-c'
       option to find a point in the domain to use for its point check of your
       inverse definition.

       You may occasionally wish to define a function that operates on	units.
       This  can  be done using a nonlinear unit definition.  For example, the
       definition below provides conversion between radius and the area  of  a
       circle.	 This  definition  requires  a length as input and produces an
       area as output, as indicated by the 'units=' specification.  Specifying
       the  range  as  the  nonnegative numbers can prevent cryptic error mes‐
       sages.

	  circlearea(r) units=[m;m^2] range=[0,]   pi r^2 ; sqrt(circlearea/pi)

       Sometimes you may be interested in a piecewise linear unit such as many
       wire  gauges.  Piecewise linear units can be defined by specifying con‐
       versions to linear units on a list  of  points.	 Conversion  at  other
       points  will  be done by linear interpolation.  A partial definition of
       zinc gauge is

	  zincgauge[in] 1 0.002, 10 0.02, 15 0.04, 19 0.06, 23 0.1

       In this example, 'zincgauge' is the name of the piecewise linear  unit.
       The  definition of such a unit is indicated by the embedded '[' charac‐
       ter.  After the bracket, you should indicate the units to  be  attached
       to the numbers in the table.  No spaces can appear before the ']' char‐
       acter, so a definition like 'foo[kg meters]' is illegal; instead  write
       'foo[kg*meters]'.   The	definition  of	the unit consists of a list of
       pairs optionally separated by commas.  This list defines a function for
       converting  from  the piecewise linear unit to linear units.  The first
       item in each pair is the function argument;  the  second  item  is  the
       value  of  the  function  at  that  argument (in the units specified in
       brackets).  In this example, we define 'zincgauge' at five points.  For
       example,  we  set 'zincgauge(1)' equal to '0.002 in'.  Definitions like
       this may be  more readable  if written using   continuation  characters
       as

	  zincgauge[in] \
	       1 0.002	\
	      10 0.02	\
	      15 0.04	\
	      19 0.06	\
	      23 0.1

       With  the  preceding  definition,  the following conversion can be per‐
       formed:

	  You have: zincgauge(10)
	  You want: in
	      * 0.02
	      / 50
	  You have: .01 inch
	  You want: zincgauge
	      5

       If you define a piecewise linear unit that is not  strictly  monotonic,
       then the inverse will not be well defined.  If the inverse is requested
       for such a  unit,  'units'  will  return  the  smallest	inverse.   The
       '--check' option will print a warning if a non-monotonic piecewise lin‐
       ear unit is encountered.

   Defining Unit List Aliases
       Unit list  aliases  are	treated  differently  from  unit  definitions,
       because	they  are a data entry shorthand rather than a true definition
       for a new unit.	A unit list alias definition begins  with  '!unitlist'
       and  includes  the  alias and the definition;  for example, the aliases
       included in the standard units data file are

	  !unitlist   hms     hr;min;sec
	  !unitlist   time    year;day;hr;min;sec
	  !unitlist   dms     deg;arcmin;arcsec
	  !unitlist   ftin    ft;in;1|8 in
	  !unitlist   usvol   cup;3|4 cup;2|3 cup;1|2 cup;1|3 cup;1|4 cup;\
			      tbsp;tsp;1|2 tsp;1|4 tsp;1|8 tsp

       Unit list aliases are only for  unit  lists,  so  the  definition  must
       include	a  ';'.  Unit list aliases can never be combined with units or
       other unit list aliases, so the definition of 'time' shown above  could
       not  have  been	shortened to 'year;day;hms'.  As usual, be sure to run
       'units --check' to ensure that the units listed in  unit  list  aliases
       are conformable.

NUMERIC OUTPUT FORMAT
       By  default, 'units' shows results to eight significant digits. You can
       change this with the '--exponential', '--digits', and '--output-format'
       options.   The first sets an exponential format (i.e., scientific nota‐
       tion) like that used in the original Unix 'units' program,  the	second
       allows you to specify a different number of significant digits, and the
       last allows you to control the output appearance using the  format  for
       the  'printf()'	function  in  the C programming language.  If you only
       want to change the number of significant digits or specify  exponential
       format  type,  use  the	'--digits'  and  '--exponential' options.  The
       '--output-format' option affords the greatest  control  of  the	output
       appearance,   but  requires  at	least  rudimentary  knowledge  of  the
       'printf()' format syntax. See Invoking Units for descriptions of  these
       options.

   Format Specification
       The  format  specification recognized with the '--output-format' option
       is a subset of that for 'printf()'.  The format specification  has  the
       form  '%'[flags][width]['.'precision]type;  it must begin with '%', and
       must end with a floating-point type specifier: 'g' or  'G'  to  specify
       the  number  of significant digits, 'e' or 'E' for scientific notation,
       and 'f' for fixed-point decimal.  The ISO C99 standard  added  the  'F'
       type  for fixed-point decimal and the 'a' and 'A' types for hexadecimal
       floating point; these types are allowed	with  compilers  that  support
       them.   Type length modifiers (e.g., 'L' to indicate a long double) are
       inapplicable and are not allowed.

       The default format for 'units' is '%.8g'; for  greater  precision,  you
       could specify '-o %.15g'.  The 'g' and 'G' format types use exponential
       format whenever the exponent would  be  less  than  -4,	so  the  value
       0.000013  displays  as  '1.3e-005'.   These  types also use exponential
       notation when the exponent is greater than or equal to  the  precision,
       so  with  the  default format, the value 5e7 displays as '50000000' and
       the value 5e8 displays as '5e+008'.  If you prefer fixed-point display,
       you  might  specify '-o %.8f'; however, small numbers will display very
       few significant digits, and values less than 0.5e-8 will  show  nothing
       but zeros.

       The  format  specification may include one or more optional flags: '+',
       ' ' (space), '#', '-', or '0' (the  digit  zero).   The	digit-grouping
       flag ''' is allowed with compilers that support it.  Flags are followed
       by an optional value for the minimum field width, and an optional  pre‐
       cision specification that begins with a period (e.g., '.6').  The field
       width includes the digits, decimal point, the exponent, thousands sepa‐
       rators (with the digit-grouping flag), and the sign if any of these are
       shown.

   Flags
       The '+' flag causes the output to have a sign ('+' or '-').  The  space
       flag ' ' is similar to the '+' flag, except that when the value is pos‐
       itive, it is prefixed with a space rather than a plus sign;  this  flag
       is ignored if the '+' flag is also given.  The '+' or ' ' flag could be
       useful if conversions might include positive and negative results,  and
       you  wanted  to	align the decimal points in exponential notation.  The
       '#' flag causes the output value to contain  a  decimal	point  in  all
       cases;  by  default,  the output contains a decimal point only if there
       are digits (which can be trailing zeros) to the	right  of  the	point.
       With  the  'g' or 'G' types, the '#' flag also prevents the suppression
       of trailing zeros.  The digit-grouping flag ''' shows a thousands sepa‐
       rator  in  digits to the left of the decimal point.  This can be useful
       when displaying large numbers in fixed-point decimal; for example, with
       the format '%f',

	  You have: mile
	  You want: microfurlong
		  * 8000000.000000
		  / 0.000000

       the  magnitude of the first result may not be immediately obvious with‐
       out counting the digits to the left of the decimal point.  If the thou‐
       sands  separator  is  the comma (','), the output with the format '%'f'
       might be

	  You have: mile
	  You want: microfurlong
		  * 8,000,000.000000
		  / 0.000000

       making the magnitude readily apparent.	Unfortunately,	few  compilers
       support the digit-grouping flag.

       With  the  '-' flag, the output value is left aligned within the speci‐
       fied field width.  If a field width greater than  needed  to  show  the
       output  value is specified, the '0' (zero) flag causes the output value
       to be left padded  with	zeros  until  the  specified  field  width  is
       reached; for example, with the format '%011.6f',

	  You have: troypound
	  You want: grain
		  * 5760.000000
		  / 0000.000174

       The '0' flag has no effect if the '-' (left align) flag is given.

   Field Width
       By default, the output value is left aligned and shown with the minimum
       width necessary for the specified (or default) precision.  If  a  field
       width greater than this is specified, the value shown is right aligned,
       and padded on the left with enough  spaces  to  provide	the  specified
       field  width.  A width specification is typically used with fixed-point
       decimal to have columns of numbers align at  the  decimal  point;  this
       arguably  is  less  useful with 'units' than with long columnar output,
       but it may nonetheless assist in quickly assessing the relative	magni‐
       tudes of results.  For example, with the format '%12.6f',

	  You have: km
	  You want: in
		  * 39370.078740
		  /	0.000025
	  You have: km
	  You want: rod
		  *   198.838782
		  /	0.005029
	  You have: km
	  You want: furlong
		  *	4.970970
		  /	0.201168

   Precision
       The  meaning  of ``precision'' depends on the format type.  With 'g' or
       'G', it specifies the number of significant digits (like the '--digits'
       option); with 'e', 'E', 'f', or 'F', it specifies the maximum number of
       digits to be shown after the decimal point.

       With the 'g' and 'G' format types, trailing zeros  are  suppressed,  so
       the  results  may sometimes have fewer digits than the specified preci‐
       sion (as indicated above, the '#' flag causes trailing zeros to be dis‐
       played).

       The  default precision is 6, so '%g' is equivalent to '%.6g', and would
       show the output to six significant digits.   Similarly,	'%e'  or  '%f'
       would show the output with six digits after the decimal point.

       The C 'printf()' function allows a precision of arbitrary size, whether
       or not all of the digits are meaningful.  With most compilers, the max‐
       imum  internal precision with 'units' is 15 decimal digits (or 13 hexa‐
       decimal digits).  With the '--digits' option, you are  limited  to  the
       maximum	internal precision; with the '--output-format' option, you may
       specify a precision greater than this, but it may  not  be  meaningful.
       In some cases, specifying excess precision can result in rounding arti‐
       facts.  For example, a pound is exactly 7000 grains, but with the  for‐
       mat '%.18g', the output might be

	  You have: pound
	  You want: grain
		  * 6999.9999999999991
		  / 0.00014285714285714287

       With the format '%.25g' you might get the following:

	  You have: 1/3
	  You want:
		  Definition: 0.333333333333333314829616256247

       In  this case the displayed value includes a series of digits that rep‐
       resent the underlying binary floating-point approximation  to  1/3  but
       are not meaningful for the desired computation.	In general, the result
       with excess precision is system dependent.  The precision affects  only
       the  display  of numbers; if a result relies on physical constants that
       are not known to the specified  precision,  the	number	of  physically
       meaningful digits may be less than the number of digits shown.

       See  the documentation for 'printf()' for more detailed descriptions of
       the format specification.

       The '--output-format' option is incompatible with  the  '--exponential'
       or  '--digits'  options;  if  the  former  is given in combination with
       either of the latter, the format  is  controlled  by  the  last	option
       given.

LOCALIZATION
       Some units have different values in different locations.  The localiza‐
       tion feature accommodates this by allowing a units data file to specify
       definitions that depend on the user's locale.

   Locale
       A  locale is a subset of a user's environment that indicates the user's
       language and country, and some attendant preferences, such as the  for‐
       matting of dates.  The 'units' program attempts to determine the locale
       from the POSIX setlocale function; if  this  cannot  be	done,  'units'
       examines  the  environment  variables  'LC_CTYPE' and 'LANG'.  On POSIX
       systems, a locale is of the form language'_'country, where language  is
       the  two-character code from ISO 639-1 and country is the two-character
       code from ISO 3166-1; language is lower case and country is upper case.
       For example, the POSIX locale for the United Kingdom is 'en_GB'.

       On systems running Microsoft Windows, the value returned by setlocale()
       is different from that on POSIX systems; 'units' attempts  to  map  the
       Windows	value  to  a  POSIX  value  by	means  of  a table in the file
       'locale.map' in the same directory, typically '/usr/local/share/units',
       as  the	default  units data files.  The file includes entries for many
       combinations of language and country, and can be  extended  to  include
       other  combinations.  The 'locale.map' comprises two tab-separated col‐
       umns; each entry is of the form

	  Windows-locale   POSIX-locale

       where POSIX-locale is as described above, and Windows-locale  typically
       spells  out  both the language and country.  For example, the entry for
       the United States is

	  English_United States   en_US

       You can force 'units' to run in a desired  locale  by  using  the  '-l'
       option.

       In order to create unit definitions for a particular locale you begin a
       block of definitions in a unit datafile with '!locale'  followed  by  a
       locale  name.   The  '!'  must be the first character on the line.  The
       'units' program reads the following definitions	only  if  the  current
       locale	matches.    You   end	the  block  of	localized  units  with
       '!endlocale'.  Here is an example, which defines the British gallon.

	  !locale en_GB
	  gallon       4.54609 liter
	  !endlocale

   Additional Localization
       Sometimes the locale isn't sufficient to  determine  unit  preferences.
       There  could  be regional preferences, or a company could have specific
       preferences.  Though probably uncommon, such  differences  could  arise
       with  the choice of English customary units outside of English-speaking
       countries.  To address this, 'units' allows specifying definitions that
       depend on environment variable settings.  The environment variables can
       be controled based on the current locale, or the user can set  them  to
       force a particular group of definitions.

       A  conditional  block  of  definitions in a units data file begins with
       either '!var' or '!varnot' following by an  environment	variable  name
       and  then  a  space  separated  list  of values.  The leading '!'  must
       appear in the first column of a units data file,  and  the  conditional
       block is terminated by '!endvar'.  Definitions in blocks beginning with
       '!var' are executed only if the environment variable is	exactly  equal
       to  one	of  the  listed  values.  Definitions in blocks beginning with
       '!varnot' are executed only if the environment variable does not  equal
       any of the list values.

       The  inch  has  long been a customary measure of length in many places.
       The word comes from the latin uncia meaning ``one twelfth,''  referring
       to  its	relationship with the foot.  By the 20th century, the inch was
       officially defined in English-speaking countries relative to the  yard,
       but  until  1959, the yard differed slightly among those countries.  In
       France the customary inch, which was displaced in 1799  by  the	meter,
       had a different length based on a french foot.  These customary defini‐
       tions could be accommodated as follows:

	  !var INCH_UNIT usa
	  yard		3600|3937 m
	  !endvar
	  !var INCH_UNIT canada
	  yard		0.9144 meter
	  !endvar
	  !var INCH_UNIT uk
	  yard		0.91439841 meter
	  !endvar
	  !var INCH_UNIT canada uk usa
	  foot		1|3 yard
	  inch		1|12 foot
	  !endvar
	  !var INCH_UNIT france
	  foot		144|443.296 m
	  inch		1|12 foot
	  line		1|12 inch
	  !endvar
	  !varnot INCH_UNIT usa uk france canada
	  !message Unknown value for INCH_UNIT
	  !endvar

       When 'units' reads the above definitions it will check the  environment
       variable  'INCH_UNIT' and load only the definitions for the appropriate
       section.  If 'INCH_UNIT' is unset or is not set	to  one  of  the  four
       values  listed then 'units' will run the last block.  In this case that
       block uses the '!message' command to display a warning message.	Alter‐
       natively that block could set default values.

       In  order to create default values that are overridden by user settings
       the data file can use the '!set' command,  which  sets  an  environment
       variable  only  if  it is not already set;  these settings are only for
       the current 'units' invocation and do not persist.  So if  the  example
       above  were  preceded  by  '!set INCH_UNIT france' then this would make
       'france' the default value for 'INCH_UNIT'.  If the user  had  set  the
       variable in the environment before invoking 'units', then 'units' would
       use the user's value.

       To link these settings to the user's locale you combine the '!set' com‐
       mand  with  the	'!locale' command.  If you wanted to combine the above
       example with suitable locales you could do by preceding the above defi‐
       nition with the following:

	  !locale en_US
	  !set INCH_UNIT usa
	  !endlocale
	  !locale en_GB
	  !set INCH_UNIT uk
	  !endlocale
	  !locale en_CA
	  !set INCH_UNIT canada
	  !endlocale
	  !locale fr_FR
	  !set INCH_UNIT france
	  !endlocale
	  !set INCH_UNIT france

       These  definitions  set the overall default for 'INCH_UNIT' to 'france'
       and set default values for four	locales  appropriately.   The  overall
       default setting comes last so that it only applies when 'INCH_UNIT' was
       not set by one of the other commands or by the user.

       If the variable given after  '!var'  or	'!varnot'  is  undefined  then
       'units'	prints	an error message and ignores the definitions that fol‐
       low.  Use '!set' to create defaults  to	prevent  this  situation  from
       arising.   The  '-c' option only checks the definitions that are active
       for the current environment and locale, so when adding new  definitions
       take  care  to  check that all cases give rise to a well defined set of
       definitions.

ENVIRONMENT VARIABLES
       The 'units' program uses the following environment variables:

       HOME   Specifies the location of your home directory;  it  is  used  by
	      'units' to find a personal units data file '.units'.  On systems
	      running Microsoft Windows, 'units' tries to determine your  home
	      directory  from the 'HOMEDRIVE' and 'HOMEPATH' environment vari‐
	      ables if 'HOME' does not exist.

       LC_CTYPE, LANG
	      Checked to determine the locale if 'units' cannot obtain it from
	      the  operating system.  Sections of the standard units data file
	      are specific to certain locales.

       MYUNITSFILE
	      Specifies your personal  units  data  file.   If	this  variable
	      exists,  'units'	uses its value rather than searching your home
	      directory for '.units'.  The personal units  file  will  not  be
	      loaded if any data files are given using the '-f' option.

       PAGER  Specifies  the pager to use for help and for displaying the con‐
	      formable units.  The help function browses  the  units  database
	      and calls the pager using the '+n'n syntax for specifying a line
	      number.  The default pager is 'more'; 'PAGER'  can  be  used  to
	      specify alternatives such as 'less', 'pg', 'emacs', or 'vi'.

       UNITS_ENGLISH
	      Set  to  either  'US' or 'GB' to choose United States or British
	      volume definitions, overriding the default from your locale.

       UNITSFILE
	      Specifies the units data file to use (instead of	the  default).
	      You  can	only specify a single units data file using this envi‐
	      ronment variable.  If units data files are given using the  '-f'
	      option,  the file specified by 'UNITSFILE' will be not be loaded
	      unless  the  '-f'  option  is  given  with  the	empty	string
	      ('units -f ""').

UNICODE SUPPORT
       The standard units data file is in Unicode, using UTF-8 encoding.  Most
       definitions use only ASCII characters (i.e., code points U+0000 through
       U+007F); definitions using non-ASCII characters appear in blocks begin‐
       ning with '!utf8' and ending with '!endutf8'.

       When 'units' starts, it checks the locale to  determine	the  character
       set.   If 'units' is compiled with Unicode support and if the character
       set is UTF-8, 'units' reads the UTF-8 definitions; otherwise these def‐
       initions  are  ignored.	 When  Unicode support is active, 'units' will
       check every line of all of the units data files	for  invalid  or  non-
       printing  UTF-8 sequences; if such sequences occur, 'units' ignores the
       entire line.  In addition to checking validity, 'units' determines  the
       display	width  of non-ASCII characters to ensure proper positioning of
       the pointer in some  error  messages  and  to  align  columns  for  the
       'search' and '?'  commands.

       At  present,  'units' does not support Unicode under Microsoft Windows.
       The UTF-16 and UTF-32 encodings are not supported on any systems.

       If definitions that contain non-ASCII characters are added to  a  units
       data  file,  those  definitions	should	be enclosed within '!utf8' ...
       '!endutf8' to ensure that they are only loaded when Unicode support  is
       available.   As	usual,	the '!'  must appear as the first character on
       the line.  As discussed in Units Data Files, it's usually best  to  put
       such  definitions  in  supplemental  data files linked by an '!include'
       command or in a personal units data file.

       When Unicode support is not active, 'units' makes no assumptions  about
       character encoding, except that characters in the range 00-7F hexadeci‐
       mal correspond to ASCII	encoding.   Non-ASCII  characters  are	simply
       sequences  of  bytes,  and have no special meanings; for definitions in
       supplementary units data files, you can	use  any  encoding  consistent
       with  this assumption.  For example, if you wish to use non-ASCII char‐
       acters in definitions when running 'units' under Windows, you can use a
       character  set  such  as Windows ``ANSI'' (code page 1252 in the US and
       Western Europe).  You can even use UTF-8, though some messages  may  be
       improperly   aligned,   and  'units'  will  not	detect	invalid  UTF-8
       sequences.  If you use UTF-8  encoding  when  Unicode  support  is  not
       active, you should place any definitions with non-ASCII characters out‐
       side '!utf8' ...  '!endutf8' blocks—otherwise, they will be ignored.

       Typeset material other than code  examples  usually  uses  the  Unicode
       minus  (U+2212)	rather	than  the ASCII hyphen-minus operator (U+002D)
       used in 'units'; the figure dash (U+2012) and en dash (U+2013) are also
       occasionally  used.  To allow such material to be copied and pasted for
       interactive use or in units data files, 'units' converts these  charac‐
       ters  to  U+002D  before  further processing.  Because of this, none of
       these characters can appear in unit names.

READLINE SUPPORT
       If the 'readline' package has been compiled in, then  when  'units'  is
       used  interactively,  numerous command line editing features are avail‐
       able.  To check if your version of 'units' includes 'readline',	invoke
       the program with the '--version' option.

       For  complete  information  about 'readline', consult the documentation
       for the 'readline' package.  Without any  configuration,  'units'  will
       allow  editing  in  the style of emacs.	Of particular use with 'units'
       are the completion commands.

       If you type a few characters and then hit ESC  followed	by  '?'   then
       'units'	will display a list of all the units that start with the char‐
       acters typed.  For example, if you type 'metr' and then request comple‐
       tion, you will see something like this:

	  You have: metr
	  metre 	    metriccup	      metrichorsepower	metrictenth
	  metretes	    metricfifth       metricounce	metricton
	  metriccarat	    metricgrain       metricquart	metricyarncount
	  You have: metr

       If  there  is  a unique way to complete a unitname, you can hit the TAB
       key and 'units' will provide the rest of the  unit  name.   If  'units'
       beeps,  it  means that there is no unique completion.  Pressing the TAB
       key a second time will print the list of all completions.

UPDATING CURRENCY EXCHANGE RATES
       The units program includes currency exchange rates and prices for  some
       precious  metals  in the database.  Of course, these values change over
       time, sometimes very rapidly, and 'units' cannot provide real time val‐
       ues.   To update the exchange rates run the 'units_cur', which rewrites
       the    files    containing    the     currency	  rates,     typically
       '/usr/local/share/units/currency.units'.  This program must be run with
       suitable permissions to write the file.	 To  keep  the	rates  updated
       automatically,  it could be run by a cron job on a Unix-like system, or
       a similar scheduling program on a different system.  Currency  exchange
       rates are taken from Time Genie (http://www.timegenie.com) and precious
       metals  pricing	from  Packetizer  (www.packetizer.com).   These  sites
       update  once  per  day,	so  there  is no benefit in running the update
       script more often than daily.  You can run 'units_cur' with a  filename
       specified  on the command line and it will write the data to that file.
       If you give '-' for the file it will write to standard output.

DATABASE COMMAND SYNTAX
       unit definition
	      Define a regular unit.

       prefix- definition
	      Define a prefix.

       funcname(var) units=[in-units,out-units]  domain=[x1,x2]  range=[y1,y2]
       definition(var) ; inverse(funcname)
	      Define  a  nonlinear  unit or unit function.  The three optional
	      keywords 'units=', 'range=' and  'domain='  can  appear  in  any
	      order.  The definition of the inverse is optional.

       tabname[out-units] pair-list
	      Define  a piecewise linear unit.	The pair list gives the points
	      on the table listed in ascending order.

       !endlocale
	      End a block of definitions beginning with '!locale'

       !endutf8
	      End a block of definitions begun with '!utf8'

       !endvar
	      End a block of definitions begun with '!var' or '!varnot'

       !include file
	      Include the specified file.

       !locale value
	      Load the following definitions only of  the  locale  is  set  to
	      value.

       !message text
	      Display  text  when the database is read unless the quiet option
	      ('-q') is enabled.

       !set variable value
	      Sets the environment variable, variable, to the specified  value
	      only if it is not already set.

       !unitlist alias definition
	      Define a unit list alias.

       !utf8  Load  the  following definitions only if 'units' is running with
	      UTF-8 enabled.

       !var variable value-list
	      Load the following definitions only if the environment variable,
	      variable	is  set to one of the values listed on the space sepa‐
	      rated value list. If variable is not set then 'units' prints  an
	      error message and ignores the following definitions.

       !varnot variable value-list
	      Load the following definitions only if the environment variable,
	      variable is not set to one of the values	listed	on  the  space
	      separated  value	list.	If  variable  is  not set then 'units'
	      prints an error message and ignores the following definitions.

GNU FREE DOCUMENTATION LICENSE
FILES
       /usr/local/share/units/definitions.units — the standard units data file

AUTHOR
				  7 June 2013			      UNITS(1)
