Shop By Category

Importance of COSC Certification in Watches: Simple Guide

COSC Certification Banner

When buying a watch, one certification can assure its accuracy and precision: the Contrôle Officiel Suisse des Chronomètres (COSC) certification.

As a potential watch owner, it’s essential to understand what this certification means and why it is important. This easy-to-understand guide will explain COSC certification, its criteria, and the benefits of owning a COSC-certified watch.

COSC Procedure Shot
Image from COSC – Source

What is COSC Certification?

COSC is an independent, non-profit organization based in Switzerland that tests and certifies the accuracy and precision of timepieces. Established in 1973, the organization has been a benchmark in the watch industry. Top brands such as Rolex and Omega proudly display the certification on their dials. COSC certification is granted to watches that pass rigorous tests and meet the required criteria, ensuring the watch is a reliable and accurate timekeeping instrument.

How Does a Watch Become COSC Certified?

To become COSC certified, a watch movement (the internal mechanism responsible for timekeeping) must undergo stringent tests over 15 days. These tests are conducted in different positions and temperatures to simulate real-life conditions. The main criteria for COSC certification include the following:

  1. Daily Rate: The watch must maintain an average daily rate of -4/+6 seconds per day for mechanical watches and ±0.07 seconds per day for quartz watches.
  2.  Mean Variation in Rates: The mean variation in rates (the difference between the daily rates) should not exceed 2 seconds for mechanical watches.
  3.  Greatest Variation in Rates: The greatest variation in rates should not exceed 5 seconds for mechanical watches.
  4.  Horizontal and Vertical Difference: The difference between the average daily rate in a horizontal and vertical position should not exceed -6/+8 seconds for mechanical watches.
  5.  Residual Effect of Temperature: The residual effect of temperature on the daily rate should not exceed ±0.6 seconds per degree Celsius for mechanical watches.
  6.  Recovery Time: The watch should return to its average daily rate within two minutes after exposure to a temperature change.

Once a watch movement has passed these tests, it is awarded the COSC certificate, indicating its accuracy and reliability.

COSC Certification
Image from COSC – Source

Benefits of Owning a COSC-Certified Watch

  1. Assurance of Accuracy: Owning a COSC-certified watch ensures that your timepiece meets the highest standards of accuracy and precision, making it a reliable instrument for daily use.
  2.  Quality and Craftsmanship: COSC certification is a testament to the quality and craftsmanship of the watch, as it signifies that the watchmaker has put in the effort to create a precise and reliable timepiece.
  3.  Increased Value: COSC-certified watches often hold their value better than non-certified watches, making them a more attractive option.
  4.  Prestige: Owning a COSC-certified watch carries a certain level of prominence, as these timepieces are produced by some of the most respected watchmakers in the industry.


COSC certification is a prestigious title for watches that meet high standards. With strict testing, advanced labs, and SAS accreditation, COSC plays a vital role in maintaining the reputation of Swiss watches worldwide.

If you have enjoyed this article, be sure to check out the rest of our blog right here.