measure for foc with the tip you will be using. i honestly have not found a lot of difference in arrow flight or point of impact by altering foc.i experimented with fletch position and foc years ago and to be honest....i think it's over rated since you've got to go out of your way to move foc out of the accepted 10%-20& range. as long as the front of your arrow is heavier than the rear.....the point will hit the target first.....lol