So I make my Glass bows Nock to Nock because of making self bows, and that is how I learned.
I measure on the back of the bow from the nock to the fade end, and add the riser length.
I have a 58" AMO recurve made in 1974, it measures
18-1/4" nock to fade on the back, 20" riser = 56-1/2"
18-5/8" nock to fade on the belly, 20" riser = 57-1/4"
58" AMO I need a 55" string
More searching I find that a 58" recurve needs to measure 55" NTN at correct brace Hight
Nuffin out of you Roy and Pat