Standard Test Method for the Determination of Percent of Let-Off for Archery Bows

It is recognized that certain designs of the cams used in the compounding systems of archery bows cause variation in the percent of let-off with change in draw length, draw weight, or both. This is true particularly with the style of cam that achieves draw length adjustment by effectively altering the length of the shooting string by any of several methods. In this case, the mid-draw length and the maximum draw weight obtainable (but not to exceed the maximum rated weight of the bow) shall be used to determine the official percent of let-off for the bow in question.

Historically, two methods have been in use to establish the percent of let-off for archery bows. The most common method uses the peak draw force and the minimum holding force read from the force-draw curve to calculate the percent of let-off. The second method uses the peak draw force from the force-draw curve and the minimum holding force from the let-down curve for this calculation. This test method defines the two methods and distinguishes between them.