Quote Chris: FOC stands for Front of Center. It's the a measurement that shows at what point your arrow balances. You can find the balance point easily, just use a pencil and try to figure out at what point your arrow balances. You want your FOC between roughly 7-15%. Some documents even say for broadheads you want to be 11% or more. Find the exact center of the arrow measured in inches and mark with a pencil. Then find the balance point of the arrow. Take the difference of the balance point from the center point and divide by the total length. This will give you the percentage. Lets say the arrow is 30" in length (including the tip or broadhead and to the throat of the nock). The center is then 15" but it balances 3" closer to the tip than the center of the arrow. The FOC is 3/30 or 10%. End Quote. I have tested my arrows and here are the results. Please feel free to give advice here. My hunting arrows are Easton Kinetic A / C 340's with four 3 inch feathers. They measured 30.8125 inches from the throat of the nock to the point of the 100 gr. Steel Force broadhead. They balanced 2.625 inches forward of the the centerline. If my calculations are correct, the FOC is 8.5%. (2.635 / 30.8125 = .085) My target arrows are Gold Tip Pro X-Cutters with three 4 inch feathers. They measured 30.875 inches from the throat of the nock to the point of the 85 gr. field point. They balanced 3.5 inches forward of the centerline. Using the same formula, the FOC is 11.3%. If I add the new Quick spin vanes to my hunting shafts, weight will be moved back. Where do I go from here? THX in advance for any tech help.