Patek Philippe 5207 Mode D'emploi page 4

The minute repeater
On demand, the minute repeater strikes the
hours, the quarter-hours, and then the minutes
that have elapsed since the last quarter-hour. The
first hammer strikes the hours on the low-pitched
gong with one strike for each hour. Subsequently,
each quarter-hour is sounded as an alternating
double strike by two hammers on both the high-
and low-pitched gongs. Finally, the second ham-
mer strikes the high-pitched gong to count the
number of minutes that have passed since the last
quarter-hour.
At 12:59, for instance, the melody consists of 12
low sounds, 3 double high/low sounds, and 14
high sounds (totaling the maximum of 32 strikes).
The tourbillon
In the course of the 18th century, watchmakers
discovered that the rate deviations of their mo-
vements were, in the final analysis, caused by the
tiny hairsprings which together with the balance
constitute the oscillator of every timepiece. Since
its center of gravity does not coincide with the
geometric center of the spring, the regular brea-
thing of the hairspring is negatively affected by the
earth's pull in any orientation except horizontal.
The tourbillon corrects this systemic "positio-
nal" error. This is done by integrating the balance
and the escapement in a hinged cage that rotates
about its axis once a minute. On this orbit, the
slightly eccentric center of gravity of the hairspring
revolves around the center of the cage every 60
seconds, so the positional error is automatically
offset by progression, regardless of the orientation
of the spring.
The perpetual calendar
with retrograde date
The perpetual calendar features an ingenious
function: a so-called retrograde date with a fly-
back hand that depending on the month and leap-
year cycle automatically flies back to the first day
of the month after the 28th, 29th, 30th, or 31st
day. A spiral spring is responsible for the fast fly-
back of the date hand. The clever mechanism was
developed by Patek Philippe in 1986 and further
refined. It requires only little energy and prevents
the flyback hand from bouncing forward after it
has jumped back to the first day of the month.
In leap years, the date hand first advances to Fe-
bruary 29 and then jumps directly to March 1 the
next day.
If the watch is worn or kept in a winder every
day, the perpetual calendar will not need to be
corrected until February 28, 2100. The year 2100
is a secular year in which the leap day is skipped
according to the Gregorian calendar.