What I would like to know is how to calculate Pp and on this feature. The formula for this is: USL-LSL/6s. For true position that would be i.e. .010-0/6*(whatever standard deviation is on the population of parts). When mmc becomes involved, the USL becomes variable. Sometimes its .025, sometimes its .0252. The method I use now is to calculate the percentage of tolerance used and then my formula becomes 100-0/6*standard deviation of the percentage. Is this correct? If not, why and what is the correct method.