ISO 4662:2017 specifies two methods for determining the rebound resilience of rubber the hardness of which lies between 30 IRHD and 85 IRHD. They are the pendulum method and the tripsometer method. With the pendulum method, a mass with a spherical end impacts a flat test piece, firmly held but free to bulge. The kinetic energy of the impacting mass is measured immediately before and after impact. With the tripsometer method, a flat test piece is impacted by a hemisphere mounted on the periphery of a disc which is supported on an axle and caused to rotate by an off-axis mass. The kinetic energy of the impacting mass is measured immediately before and after impact.