I don't really know, I've never measured. The concept is, you have your cases sized, and the sized cases fit snug around the trim pilot. The end of the pilot goes through the flash hole and hits the lock stud.

In theory, everything is up tight against something else, so trimming should be repeatable. The only thing I can think of that would throw you off is a burr or a slightly bent case rim that affects your length a little bit, but that would probably get you with other systems too.