For legacy Circularity and Cylindricity dimensions as well as a Location dimension's RN Line, the feature solution is used to compute the dimension. By default this is Least Squares. However, you can choose to solve the feature using Minimum Separation, Maximum Inscribed, Minimum Circumscribed, or Fixed Radius regression algorithms.

FCF Circularity and Cylindricity dimensions on the other hand are computed using the Chebyshev algorithm (Min/Max) as required by the Y14.5 standard. Because of the change in calculation, Circularity and Cylindricity FCF dimensions will generally compute to a slightly smaller value than their legacy counterparts.