I used this scale to test 2 different bows, one was set at 62.2 lb from the factory according to the shipping label. According to the scale it was about 50 lbs. The other bow I tested was set at 70 lb and it read about 55 lb on the scale. If there is a way to calibrate this scale it is a good deal, but since there is not instructions that came with it, all I can assume is the only way is to change the spring, which I am not going to do, instead I will probably just return it. Which is too bad, because I really liked the idea of a portable bow scale like this.