The minimum zone separation functional describes global shape characteristics of form tolerance for a metrological artefact and is computed from measurement data described by a simple planar polygon. The nominal (perfect form) geometry is realized by a convex polygon. An analytic expression to compute the minimum zone measure is derived in the case of a regular polygonal perfect form, and a geometric procedure is adopted in the solution for a convex perfect form. A minimum area difference measure is introduced, and the geometry of typical separation functionals is examined. Separation measures are also calculated for nominal convex polygonal components described by a discontinuous (incomplete) data set such as commonly occurs with keyways, flats, and partial arcs. Computational considerations, including algorithm performance, are also addressed. © 1998 Elsevier Science Ltd. All rights reserved.