The more the better, especially your sight radius and your peep height at full draw down to your arrow shaft. Speed and total weight of your arrow. In my experience you need as much as you can get. If you dont have someone to measure your peep height and sight radius or a drawing board I just sat on the floor and put my feet on the riser and drew it back and took my measurements that way. It works, I was suprised at how accurate the tapes are, if you can shoot thru a chrono that speed will work for you better, but the computer calculated speed can work for you too.