I'm sure you will get a lot of replies, but the way I use it is to sort of "reverse engineer" it. I tune my bow, starting with what is recommended and varying length and point weight as necessary. Once it is shooting right, I put the specs into the calculator and then use the form factor (-15, +15) to get the bow dynamic spec s to match the arrow dynamic specs. At that point, I can use the calculator to check out different brands, spines, etc and know they will be spot on, or VERY close to it.