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### Generalities

The usual objective of dimensioning is to convert a CAD-construction into a manufacturing-ready drawing. In a parametric system, dimensioning additionally controls the geometry through the changing of dimension values.
In order to keep these two totally different uses for dimensioning transparent for the user, SISCAD-P offers two separate types of dimensions:

- Reference dimensions - green
  Reference dimensions (informational dimensions) are the normal type of associative dimensions known in all CAD-systems: they change their values when the geometry changes. This type of dimensioning refers to the current geometric configuration.

- Parametric dimensions - yellow
  Parametric dimensioning takes over the control of geometry when you are working parametrically. In this type of dimensioning, the dimension value determines the geometric configuration, i.e. the geometry automatically adapts to the change of the dimension value.
  The generation of parametric dimensions is not fundamentally different from the generation of reference dimensions; please note however that not all parameters are supported.

The important difference in the functionality of the two types of dimensioning is underlined by SISCAD-P in that it puts the two types on separate layers and assigns them different colors:

> Parametric dimensions are yellow, reference dimensions are green.

You switch between the two types of dimensioning using the icon in the info parametric window of the main menu. The color of that icon informs you on the current state of dimensioning.
Dimensioning uses the WYSIWYG principle. That means that as soon as the objects to be dimensioned are selected, the dimension can be positioned in the desired place with the cursor. The entering of further parameters is immediately taken into account in the look of the dimension.