The Reference 720 Pocket Chronograph uses a high-beat movement to provide 1/10 second timing. The chronograph second hand rotates around the dial in 30 seconds, rather then the usual 60 seconds.  Notice the two scales on the dial, 0 to 30 seconds in black and 30 to 60 seconds in red.  The clutch / intermediate wheel has two wheels, the smaller one is driven by the fourth wheel and the larger ones drives the chronographs seconds hand (center wheel) at twice the normal speed.  The Reference 720 pocket chronograph is shown only in Heuer’s 1936 catalog, suggesting that it was produced for a relatively brief period.