What Are COSC Certified Watches?


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What Are COSC Certified Watches?

If you have been part of the watch world for long, you may have come across the team ‘certified chronometers’. Alternatively, brands dub them as COSC certified watches as well. This special certification represents that the watches have the utmost accuracy and precision.

While many brands tend to market their timepiece as the most accurate watch, it is not actually always the case as there is no way of confirming this before buying. Whereas, watches with the COSC certification, on the other hand, go through intense testing. And, in the end, only those who qualify all the rounds get the certified chronometer tag. Essentially, this implies that these watches are as accurate as the brand claims them to be.

On this basis, we dive deep into what COSC certified watches are and how the certification takes place.

One can easily get confused with the terms chronometer and chronograph, check out our article to understand the difference and functions of these features.

Who is COSC?

Set up in 1973, the Official Swiss Chronometer Testing Institute is a non-profit organization based in  La Chaux-de-Fonds, Switzerland. Driven by the intention to serve the public interest, laboratories from the five major watchmaking cantons in Switzerland along with the Federation of the Swiss Watch Industry oversee the quality and testing of Swiss-made watches.

This certification, given by the COSC, guarantees the highest quality of watches by measuring and verifying the accuracy and precision of the movements. The standards of testing, governed by the Swiss Accreditation Services, follow quality control per ISO 17025 & 17065. Although millions of watches go through testing every year, according to the COSC website, only about 6% of exports from Switzerland get the certification. This shows the rigor and extent of these testing to ensure the correct quality of the watches.

Why do we need to test accuracy?

A majority of industries that depend on accurate timekeeping rely on these chronometers. We noted in the article on automatic movement accuracy that most mechanical watches or automatic watches have an accuracy of up to +/- 20 seconds a day. The reasons for this variation can be any – friction between the components, moisture build-up, extreme weather conditions, gravity, or magnetic forces.

For instance, if you are a doctor, or diver, or pilot, every second counts in a day. And, a variation of over 20 seconds a day can have lasting consequences. This is where the COSC certification comes into play. Watches with COSC certification have only up to +6/-4 seconds daily variation, some of the lowest recorded ever in all history for mechanical watches. The certification gives the user the guarantee that they can rely on the time with utmost trust and precision, giving these watches an edge over those without any certification.

While COSC certifies only Swiss watches, there are other such organizations in the world such as the Japan Chronometer Inspection Institute, Glashütte of Germany, and French Observatoire de Besançon bested with the responsibility of certifying watch accuracy.

Process of COSC Certification

Watches that apply for a COSC certification go through days of testing period on various positions and temperature settings. Given the nature of the expensive testing, not all watchmakers have the option to apply for the certification. For this reason, only luxury watchmakers with high-quality chronometers, often carefully hand-assembled, get certified.

The process of certification goes through four stages: setting the procedure, picking a test program, certification, and finally, delivery. Moreover, COSC only tests movements and timekeeping instruments, and not the finished watch product in itself. For watch brands, this means they test their movements and build these movements into fully engineered watches on being certified.

Mechanical watches with balance spring oscillators and quartz movements with oscillators are eligible for getting certified. Mechanical wristwatches and pocket watches go through 15 days of continuous testing. Clocks go through 9 days of testing, and quartz movements go through 7 days of testing. Including weekends, these measurements from the test record their functions.

For mechanical wristwatches with ISO 3159, only upon meeting these seven measurement rates, the final certification will apply: average daily rates, mean variation, greatest variations, the difference in horizontal and vertical rates, largest variation, variations on temperature, and rate resumption.

As you see, the COSC certification process is not cheap, nor is the process of building watches eligible for COSC certification. Consequently, watches with the certified chronometer tag have a high value and are not easily affordable for all.

Top COSC Chronometers

In this section, we highlight some top COSC chronometers of all time.

Omega Seamaster

Omega Seamaster CO‑AXIAL MASTER CHRONOMETER 42 MM DIVER 300M
Omega Seamaster Co‑Axial Master Chronometer 42 MM (Image: Omega)

Omega uses the term ‘Master Chronometer’ on the face of the watch to denote all those movements with COSC certification. These movements go through eight different types of tests to raise their standard on precision, durability, water resistance, and anti-magnetic properties. One such is the Omega Seamaster Collection.

More particularly, the Planet Ocean edition under this collection is an embodiment of  Omega’s promise of an ultimate watch. Hosting the in-house movement along with Omega’s in-house metal to design the watch, the Planet Ocean watch is your reliable companion in the sea with -4/+6 seconds per day variation.

Rolex GMT Master II

The Oyster Perpetual GMT-Master II in Oystersteel and Everose gold
Oyster Perpetual GMT-Master II in Oystersteel and Everose gold (Image: Rolex)

Rolex needs no detailed introduction. Every person dreams of owning a Rolex for its unparalleled superiority. Naturally, all of Rolex’s timepieces come with COSC certification as well. On the face of the watch, the brand features the Superlative Chronometer Official certification right above 6 o’clock.

For this article, we look at the GMT Master-II. Hosting the 3285 caliber, the movement shows a daily variation of just +/- 2 seconds only – one of the most accurate mechanical movements available today!

Zodiac Limited Edition Super Sea Wolf

Limited Edition Super Sea Wolf 68 Saturation X Andy Mann Watch
Limited Edition Super Sea Wolf 68 Saturation X Andy Mann Watch (Image: Zodiac)

If you are looking for a relatively affordable COSC certified watch, Zodiac can be a worthy option. Inspired by their 1970 World Timer watch, this timepiece is a modern take on its retro watch. Curated for the underwater adventure spirit, the Zodiac takes into consideration the needs of a diver in designing this timepiece.

This limited edition watch, designed in collaboration with the famous photographer Andy Mann, showcases horological superiority with its design and styling. With the certified chronometer, rest assured this watch will last you a lifetime!

Longines Record

Record collection Watch by Longines
Longines Record Collection Watch (Image: Longines)

Reflecting on the quintessential timeless design, the Longines Record collection features certified chronometers as part of its collection. Designed with the L888.4 caliber, the watches part of this collection exemplify simple yet elegantly sophisticated styles. Most of all, Longines is another good affordable luxury watch option that can go down generations after you!