I've been missing all the action here, especially some important math lessons.

To give my version on what Tom said above (thanks Tom):

2*SQRT(X*X+Y*Y) is only good for circles and 2D points. The more general (but still not always correct) interpretation I was using is twice the Euclidean ;-) distance from nominal is the actual TPD. Evaluating the surface profile tolerance is one-dimensional problem so instead of using 2*SQRT(DEV*DEV) I used 2*ABS(DEV) where DEV is the max deviation for the whole surface regardless of sign. And don't write back to me explaining that the problem is 3D, because I said EVALUATING not calculating.

Reports are done for different people and for different reasons. In Duane's question the tolerance is bilateral surface profile, the nominal is zero, the tolerance is 1.0mm. What should the actual be in your PPAP report? As I understood he was asking to quantify the error on the whole feature and put a single number there. If you have two million points scanned with a laser and you need to report to your customer if the part is good how many pages is your report?

George K.