The Ape Index is a way to compare a person's arm span to their height, typically calculated by subtracting height from arm span. This measurement is commonly used in sports like climbing, swimming, and martial arts, where having a longer reach can be advantageous. A positive Ape Index—meaning the arm span is greater than the height—is often seen as helpful for tasks that require reach or leverage. Although it's not a precise predictor of skill, the Ape Index is a popular metric for identifying potential physical advantages.