A relatively simple and cheap, but effective design for a chronograph
with a split-second hand, first patented in 1948.
As in the conventional split-seconds chronograph, a second arbor
goes through the cannon of the chronograph hand. This arbor has
a stud at its end. The 2 hands are connected by a coiled hairspring,
the chronograph-hand carrying the split-secondes hand with it. A
pin under the chronograph-hand prevents the split-seconds hand overtaking
it. A button in the crown controls a brake that acts on the stud,
stopping the split-seconds hand ( to take an intermediary time ),
while the chronograph-hand keeps running. Releasing the button allows
the spring to bring the 2 hands together. The maximum interval for
intermediary times is 60 seconds, because the pin on the running
chronograph-hand comes up against the stationary split seconds hand
after 1 minute.