Conditions which movements must meet to fulfill the chronometer standard.
Watches or movements with particularly accurate running, confirmed
by an official certificate, are designated chronometers. Chronometer
movements have to be given a serial number to ensure that the
certificate and the movement can be uniquely matched. Chronometer tests
are currently carried out and documented almost exclusively by the
C.O.S.C. (Contrôle Officiel Suisse des Chronomètres, an independent
public-service organization in Switzerland). Just recently, however, the
Landesamt für Meß- und Eichwesen Thüringen (Thuringian State Office for
Measurement and Calibration) in Glashütte has started offering
chronometer tests as the accreditation office of the German Calibration
Service in Germany.
The chronometer quality of a mechanical watch movement is determined
in part by the special workmanship of certain movement components,
partly by precise regulation of the watch. We only use the highest
quality products provided by Swiss movement manufacturers in Sinn
watches. Basically all these movements can be regulated as chronometers.
If desired, our watches can be given a fine-adjustment, i.e. they are
of chronometer quality, but are supplied without a certificate.
The specifications of a mechanical chronometer movement include a
number of rate accuracy aspects: e.g. the effect of position on the
rate, the stability of the rate in each individual position and the
temperature dependency of the rate. There is an international standard
(ISO 3159) for mechanical movements which correspond to national
standard systems (DIN 8319, part 1 and NIHS 95-11).
Because the accuracy of a mechanical watch generally depends on its
spatial orientation in the Earth's field of gravity, five test positions
for observing the escapement are distinguished (e.g. "dial top", "dial
bottom" etc.). The mean of the accuracy values measured in the five
test positions should remain within a range of -4 to +6 seconds per day
(24 hours) at room temperature (23ºC). This standard, by itself, is not
particularly exacting and would probably be fulfilled by any modern
mass-production caliber. However, a chronometer movement must also
achieve this mean value with no appreciable accuracy differences between
the individual positions. The largest accuracy difference between an
upright and horizontal position (more precisely: between "crown left"
and "dial top") should be no more than -6 to +8 seconds per day. For the
remaining positions: each individual position value should not differ
from the average of all five positions by more than 10 seconds per day.
Further demands are placed on the stability of the accuracy in each
individual test position. The watch should not deviate by more than 5
seconds per day in any given position (at a constant temperature of
23°C). The mean of the deviations observed in the individual test
positions should also be no greater than 2 seconds per day. Critical
demands are also placed on the temperature dependency of the watch’s
accuracy. The watch’s accuracy is tested within a temperature range of
8°C to 38°C. The deviation per degree Celsius and day should not exceed
+/- 0.6 seconds. Finally there is a test to ensure that the watch
regains its accuracy at 23°C, after the temperature change. In a given
test position, the accuracy may not differ from the mean accuracy in
this position measured before the temperature change by more than +/- 5
seconds per day.
In chronograph movements, the accuracy difference is checked with
the stop function turned on and off. All accuracy measurements are
carried out without the use of an electronic timing machine, i.e. the
time is read off directly after 24 hours as measured on a test dial. The
entire chronometer test takes a total of 15 days.
Up to now there has been no international standard (ISO) for quartz
chronometers. In the meantime, the technical possibilities of series
production have overtaken the requirements of the Swiss and German
standard systems (see e.g. DIN standard 8319, part 2, from 1978). In
2001 the Swiss testing organization C.O.S.C. therefore formulated new
criteria for its own testing practice. This placed more stringent
requirements on quartz chronometer movements. The test criteria are
designed so that quartz movements without special temperature
compensation cannot pass the test.
At SINN, we use thermo-compensated ETA movements with a quartz frequency of just over 32 kHz in our UX and 434 models. Although quartz movements with an even higher running accuracy are technically possible in the form of mega-Hertz oscillators, they were only produced temporarily and in small quantities due to their high power consumption and high manufacturing costs.
Due to their temperature compensation, the ETA quartz movements we use are around twenty times more accurate than a conventional quartz movement regulated to room temperature and are currently the most accurate autonomous wristwatch movements.