Patek Philippe CALIBRE CH 28-520 IRM QA 24H Mode D'emploi page 11

the ch 28-520 irm Qa 24h chronograph
caliber
is a self-winding mechanical movement
with a flyback column-wheel chronograph, power-
reserve indicator, Annual Calendar, and day/night
display. It beats at a frequency of 28,800 semi-
oscillations per hour (4 Hz), assuring an extremely
constant balance amplitude and high rate accuracy.
The winding power is delivered by a heavy, unidi-
rectional 21K gold rotor. The chronograph caliber
is based on the venerable column-wheel principle
for controlling the start/stop commands. However,
it differs from classic Patek Philippe column-wheel
chronographs by virtue of a remarkable innova-
tion: the clamps do not control the engagement
of a lever-mounted clutch wheel with the chrono-
graph 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 seconds hand without affecting the rate
accuracy of the watch. For this reason, the sub-
sidiary seconds dial customarily found in many
chronographs is no longer needed.
TradiTion and
innovaTion
in perfect harmony
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