The USGA/R&A pendulum test that clocks, in millionths of a second, how long a ball stays on a clubface at impact — the check against illegal 'trampoline' spring-like effect in drivers. The legal limit is 239 microseconds, with an 18-microsecond test tolerance allowing a measured reading up to 257 before a club is ruled nonconforming. A steel ball is swung into the face's center and the contact time is timed electronically; faces built right up to that line are common, since more face flex means more ball speed for the same swing. CT replaced the older coefficient-of-restitution (COR) test in 2004 because it's easier to measure portably at tournaments.

The USGA/R&A pendulum test that clocks, in millionths of a second, how long a ball stays on a clubface at impact — the check against illegal 'trampoline' spring-like effect in drivers. The legal limit is 239 microseconds, with an 18-microsecond test tolerance allowing a measured reading up to 257 before a club is ruled nonconforming. A steel ball is swung into the face's center and the contact time is timed electronically; faces built right up to that line are common, since more face flex means more ball speed for the same swing. CT replaced the older coefficient-of-restitution (COR) test in 2004 because it's easier to measure portably at tournaments.