When you draw back all the way, letoff takes effect. Letoff is best described as a decrease in the weight you hold. When you draw all of the way back you will notice that you are holding less weight. This is letoff. If you have 80% letoff you will hold less weight than a bow with 50% letoff. A 100 pound bow with 80% letoff will mean you will hold back 20 pounds at full draw. A 50% letoff bow at 100 pounds will mean you hold back 50 lbs.