ABSTRACT
There are four form characteristics. They are flatness, straightness, circularity and cylindricity. All controlled features are individual and are not related to datums. They are assessed by comparison to a perfect geometric counterpart of themselves. Before these geometric characteristic tolerances are assessed for compliance, each controlled feature must conform to its limits of size. Surface form controls require all elements of the controlled surface or the controlled portion of a surface toreside within the tolerance zone. Flatness is a surface form control. A perfectly flat surface is defined as having all its elements in the same plane. Flatness feature control frames create a tolerance zone not related to any datums. Straightness is a form control that may be used as a surface, derived median line or derived median plane control. Circularity is a two dimensional surface form control. The surface is assessed to determine that all circles that make up the surface being controlled are within the given circularity tolerance.
