mlaubner, I simply shoot my chosen arrow through the chrono and then weigh the arrow. My present deer stomper does 254 fps with a measured 540 grain 2315 XX78 tipped with a Muzzy 115 grain head. 254x254x540 divided by 450240=77.38 foot pounds of K.E. from a 29 inch draw and 66 pound bow. I really like the way these heavier arrows perform with this set up compaired to my 457 grain carbons. The bow is quieter and has less vibration, just what I' ve found to shoot with extreme accuracy