I agree Len. They did leave a lot out. The paragraph was not very technical. And any "eyeball" method of getting to centershot will only get you close depending on who is doing the "eyeballing".
One other point that was mentioned which to me is the meat and potatos of the paragraph this:
There is only one place for the rest to be set. That is on the true center shot. If you are expecting the arrow to come out of the bow dead straight, the only way this can happen is if the rest is dead inline with the travel of the string.
Although they leave out how to identify centershot 100% in the paragraph, and leave out a lot of the variables, I believe this is a true statement.