FOC stands for "Front of Center" which is a term used in archery to describe the distribution of weight in an arrow. Specifically, the FOC is the percentage of an arrow's total weight that is located in the front half of the arrow. A higher FOC means that more of the arrow's weight is located towards the front, which can result in improved arrow flight and accuracy. It can be calculated by measuring the distance between the center of gravity (CG) and the front of the arrow (F) and dividing that by the total length of the arrow (L). The formula is (F/L)*100 = FOC.   An arrow with a high FOC will be more stable in flight, but it will also be slower. An arrow with a low FOC will be faster but less stable. A good FOC for hunting arrow is around 10-15% and for target archery is around 8-12%.   It is important to note that archery equipment and setup is a very personal thing, and what works best for one person may not work as well for another. It is important to experiment with different FOC levels and find what works best for you.