You may want to try these links. It will help to explain and determine your FOC.


http://lmariana.wso.net/foc.htm
http://homepage.ntlworld.com/joetapley/foc.htm
http://home.att.net/~sajackson/arrowtools.html

I usually keep my hunting setup with fixed bladed braodheads around 12-15 FOC. these seem to work best for my setup. How can you adjust for FOC? If you want a higher FOC, you would add a heavier tip, or wieght, or decrease the weight of your fletchings. If you want a lower FOC, you would do the opposite.