The tolerances applied to the feature or feature of size do not control all aspects of form. The form of a feature or feature of size can be constrained in one of the following ways:
- A size dimension applied to a feature of size.
- A form geometric tolerance (flatness, straightness, circularity, or cylindricity) applied to the surface of the feature
- A non form geometric tolerance applied to the surface of the feature. For example, perpendicularity applied to a planar surface imposes an equal implied flatness control to that surface. However, the tangent plane modifier eliminates the form control that would be imposed by a geometric tolerance.
It is good practice to specify the limits of form for each surface of the model either explicitly or implicitly.