COSC certification

What is a CERTIFIED CHRONOMETER watch?


The mention « certified chronometer » ensures that the movement of your BRELLUM watch is adjusted to an average daily rate criteria of -4/+6 seconds per 24 hours achieving 99.99% accuracy (ISO 3159). This absolute guarantee of reliability and precision is given out by the Contrôle Officiel Suisse de Chronométrie (COSC). Indeed, only 6% of the total Swiss production which is exported enjoys this distinction.


Which authority officially certifies your CHRONOMETER watch?


The Contrôle Officiel Suisse de Chronométrie (COSC) is an independent and official body which is recognized by the Swiss State. Its laboratories and watch certification offices are all based at Bienne in Switzerland at Locle and Saint-Imier. Each one of them has "Service de Calibration Suisse" accreditation.

What are the test conditions like that are carried out by the COSC?


The COSC carries an exhaustive examination on each movement through a range of tests lasting 15 days in accordance with the ISO 3159 standard.

The movements undergo individual daily tests during these 15 days according to a defined program of tests in five positions and at three different temperatures (8°, 23°and 38°C). Each day and including Saturday and Sunday, the instruments are measured and reassembled. Seven eliminatory criteria are calculated based on these measurements.

What are the COSC’s 7 main criteria for measuring success?


  • average daily rate
  • average variation of rate
  • the greatest variation of rate
  • the difference in rate between the watch’s horizontal and vertical positions
  • the greatest difference in rate
  • the precision of the rate in the event of temperature variations
  • rate recovery

If and only if the 7 criteria are met,

the movement is officially « certified chronometer ».