I obviously am not making myself clear. I know how to do a compression test. I know examining the cylinder for the source of leakage is more important. However for years we did compression tests with a tester that did not have a calibration orifice. Why was that changed? How was the decision to change made? If the size of the orifice is arbitrary whose arbitrary? I repeat I am in favor of the present system of compression testing. I agree with the comments made concerning test limitations. I am just trying to find out the history of the procedure changes.