That is one way of measuring draw length. I just got back from bernie pellerites shooting school and he tought me the best way to measure it. I might get some crap for this but here we go anyways
strech your arms out and measure your wing span then devide it in half and subtract 7.5''
(if you have abnormaly short or long fingers it will vary a little)
it sounds kinda strangr but trust me it works.