ASTM F1880-09(2013)

4.1 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.

4.2 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.

1.1 This test method covers the procedure to be used to determine the percent of let-off for archery bows.

1.2 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.