What is an ideal Cpm value?
Generally there is no “ideal.” Bigger is always better. The difference in Cpm as defined in SQCpack is in the calculation of the stand deviation or variance term. The standard deviation for Cpm is based on using the target value rather than the mean which will make sigma(pm) larger and Cpm smaller when the process is not centered on the target value. You could say “ideally” the process should be centered in the specification making Cpm = Cp. However, Cp might only be 0.80 which clearly is not “ideal.” Gordon Constable Ph.
