Charles Leven's practice driver was covered under a British patent dated July 28, 1921.  It has a built in mechanism that measures how far a golfer's practice swing would have hit a golf ball.  This mechanism, located in the top of the head, operates on the principle of centrifugal force with a weight and ratcheting device inside the head.  Pushing the button on the back of the head would reset the mechanism to zero, ready to measure the next swing. 

The example offered here is in tact, but is missing three of the four tiny screws that hold the mechanism in place on the top of the head. The 42 1/4" shaft and lather-wrapped grip are original as is everything else on this club. Even thought the mechanism has likely seized up, the club still represents a mechanical marvel in the world of antique golf clubs.