Seems the default for the CMM-Manager is Least Squares for measuring diameters. Our supplier uses Max Inscribed. The 6061 T6 aluminum component being supplied has 2.500-7.000 inch+/-0.005 inner diameter with a depth of 0.200-0.300 inches +/-0.005. Our company has always used least squares and 6 points to measure the ID of these components on a manual CMM with a Renshaw PH8 and TP2 probe. 

We have considered using Max Inscribed, but for a manual CMM only measuring 6 points would that method yield better accuracy? I could see how Max Inscribe would be useful for deeper diameters, but for this application I do not think it is necessary. We have not run into an issue fitting the component to its application using least squares that I am aware of.