To see how accurate the mesurement has to be simply put in a few different numbers and see how different they come out.
I beleive the most accurate way to measure the scope height is to take the rifle out of the stock, use a caliper and add up the following numbers:
A) measure the diameter of the chamber under the scope tube and devide by 2
B) Measure the distance beween the scope and the chamber.
C) Measure the outside diameter of the scope tube and devide by 2
I used to re-load but now I "hand-load".
-- Well, at least I try