Patek Philippe CALIBER CH 28-520 QA 24H Manual Del Usuario página 4

The CH 28-520 QA 24H chronograph caliber is
a self-winding mechanical movement with a flyback
column-wheel chronograph, Annual Calendar, and
day/night display. The Annual Calendar Chrono-
graph is based on the venerable column-wheel
principle for controlling the start/stop commands.
However, it differs from classic Patek Philippe col-
umn-wheel chronographs by virtue of a remarkable
innovation: the clamps do not control the engage-
ment of a lever-mounted clutch wheel with the
chronograph train, but instead act on a disk clutch
that transmits (chronograph running) or interrupts
(chronograph stopped) the power between the fourth
wheel and the chronograph hand. This is a highly
reliable solution that makes it possible to use the
chronograph hand as a continuously running second
hand without affecting the rate accuracy of the watch.
For this reason, the subsidiary seconds dial customar-
ily found in many chronographs is no longer needed
on Patek Philippe's Annual Calendar Chronographs.
5