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Quartz movements

The COSC also certifies quartz chronometers. Since no international standard currently applies to the electronic quartz watch, the COSC has established a test requirement for quartz chronometers based on the ISO 3159 standard. This prescription that certifies their performance as it does for the mechanical chronometer.

In absolute terms, a quartz movement is more precise than a mechanical movement. In reality, quartz is more inconstant, because it is very sensitive to temperature and humidity, which can significantly alter its operational regularity. High quality quartz is therefore equipped to adjust automatically to the frequency of the oscillator according to the ambient conditions. It must be encapsulated in an absolutely watertight manner so as not to be sensitive to moisture.

Minimum Requirements (for Quartz Oscillator Wristwatches) - Type IV 

Symbol

Criterion

Limite[s/d]

Avg R

Average daytime rate at 23°C

± 0.07

MT8

Rate at 8°C

± 0.20

MT38

Rate at 38°C

± 0.20

SM

Rate stability

0.05

R

Rate resumption

± 0.05

Ht

Humidity – temporary effect​       

± 0.10

 

To take into account the technological characteristics of these products, the COSC has adapted its tests and the precision requirements. To acquire the COSC label, a quartz instrument must benefit from thermo-compensation and rigorous encapsulation. Each quartz chronometer is tested for 13 days, in one position, at 3 different temperatures and 4 different relative humidity levels. The criteria are less numerous, but the tolerance levels are much more stringent.