Pinwheel is not just right, he is absolutely and indisputably right. Any draw-length method other than measuring the length of shaft when pulled on a bow, is a rough estimate. In fact, I will go a step further. Because bow grips vary, pulls vary, anchors vary vs. draw-weight, and how a person's hand sits in the grip, I firmly advocate that a person's DL be established and mated to the/each bow that he or she will be shooting.