A golf ball only stays on the club’s face for a fraction of a second, but that small amount of time determines the fate of the shot. “We’re trying to maximize the efficiency of the collision,” says Brian Bazzel, VP of Product Creation for TaylorMade. The USGA tests this variable with a pendulum-like device that measures the spring-like effect that occurs when the ball hits a club face. Despite its metal construction, the face of a driver acts a bit like a trampoline, springing the ball away after flexing at impact. “The pendulum is dropped against the face and it measures the time the ball is in contact with it in microseconds. The limit is 239 microseconds, but they give you about 18 microseconds of tolerance.” This test measures a variable called characteristic time, and it replaced an older test, which measured the absolute coefficient of energy transfer.