are you using the dynamic spine calculator? if so it has spots for the bows info and your arrows and you just mess with lengths/weights until the numbers are close to matching. a spine tester will only really give you a starting point, as dynamic spine changes once you add a broadhead, fletching and nock, etc, then length comes into play as well.how deep your shelf is also affects it to some extent,if the arrows tend to hit opposite the side of your shelf they are spined weak, the same side they are strong. i use the calculator for rough tuning and go from there, but it is usually very close, even got arrows tuned to my bendy handle bow that is 1 1/2" wide at the arrow pass.