What's a chronometer?

From Jacobs the Jewellers's watch range, all Bremont timepieces are chronometers. A chronometer is a watch that meets exacting quality control standards. The standard is set by the Swiss Official Chronometer Control (Contrôle Officiel Suisse des Chronomètres) and inspects watches to ensure they are of the highest standard. The standard used is the European standard ISO 3159. The reason for having such accuracy is that a chronometer may be used for navigation purposes used in conjunction with the stars. The COSC also has standards for quartz watches.

The measures are mecahnically:

• Average daily rate: -4/+6
• Mean variation in rates: 2
• Greatest variation in rates: 5
• Difference between rates in H & V positions: -6/+8
• Largest variation in rates: 10
• Thermal variation: ± 0.6
• Rate resumption: ± 5

COSC have developed their own standard for testing quartz chronometers with eight eliminatory criteria:

• Average daily rate at 23 °C: ± 0.07
• Rate at 8 °C: ± 0.2
• Rate at 38 °C: ± 0.2
• Rate stability: 0.05
• Dynamic rate: ± 0.05
• Temporary effect of mechanical shocks: ± 0.05
• Residual effect of mechanical shocks: ± 0.05, 200 shocks equivalent to 100 G (981 m/s²)
• Rate resumption: ± 0.05

Measurements are based on a time base established by two independent atomic clocks synchronised on GPS time.

Some watches meet this standard, all Bremont watches do.