In this paper, we describe techniques for evaluating the uncertainties associated with the assessment of form error, i.e., the departure from ideal geometry of a manufactured part, in coordinate metrology. The techniques take into account measurement uncertainty, sampling effects due to the fact that the form error is determined from a finite set of coordinate data points, and the spatial correlation of the form errors. The techniques are designed to be practical, without the need for complex computation.

Manufactured parts are affected by size and form errors, which need to be assessedagainst geometrical and dimensional tolerances in order to meet the functionalrequirements they have been conceived for. The compliance assessment of workpieces withspecifications depends on measurements and is unavoidably affected by several uncertaintycontributions. According to the geometrical product specifications and verification (GPS),measurement uncertainty consists of method and implementation uncertainty. Literatureproposes different approaches for the evaluation of implementation uncertainty, however astandardized method has not been yet achieved. This paper makes an analysis of the variouselements to be considered when choosing a specific approach: in the implementationuncertainty of circular features. The most common manufacturing signatures affectingcircular profiles were considered, together with the number of points necessary for areliable estimation of implementation uncertainty.