Front of Center...it pertains to the balance point of the arrow which will determine the trajectory. For hunting arrows it is recommended to have a minimum of 10 - 15% FOC to reduce planing. For aluminum target arrows 7 - 9%, 9 - 11% for A/C/C target arrows, & 11 - 16% for carbon target arrows.

Formula:

FOC % = [100 x (A-L / 2)] / L


A = distance of bottom of nock groove to the balance point of the finished arrow (including point, nock and fletching)

L = correct arrow length (bottom of nock groove to end of shaft)