Mike may be right about the single format backs, but the 120/220 are a little bit different. It seems that way with the Mamiya power backs as well. There is no accurate way to do this with a split film back for several reasons.
1. One has paper and the other does not. Differing end roll thicknesses.
2. Film bases can be of different thicknesses across different manufacturers.
A reversing pressure plate does not recalibrate any of this either.