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What is COSC Certification in Watches? The Mark of Swiss Precision

Sekvens Journal

If you’ve found yourself confused by the plethora of watch-related terms, don’t worry; you’re not alone. In this post, we’re tackling a commonly seen yet often misunderstood acronym: COSC.

What COSC actually means

Contrôle Officiel Suisse des Chronomètres, or COSC for short, is French for the Official Swiss Chronometer Testing Institute. This Swiss-based, non-profit organization is the ultimate authority that certifies the precision and accuracy of wristwatches manufactured in Switzerland. COSC certification is essentially the horological equivalent of a seal of approval from the highest echelon of Swiss precision and craft.

Now, let’s clear up a bit of confusion. The words ‘chronometer’ and ‘chronograph’ often get mixed up. In simple terms, a chronograph is a feature within a watch that allows you to measure time intervals, like a stopwatch. A chronometer, on the other hand, is a high-precision timepiece that, if made in Switzerland, must be COSC certified to flaunt that prestigious title.

Squale 1521 COSC complete set with box and certificate
Squale 1521 COSC complete set with box and certificate

A Closer Look at COSC

Established in 1973, COSC is the product of a collaboration between five Swiss cantons: Bern, Geneva, Neuchâtel, Solothurn, and Vaud. It operates through three laboratories located in Biel/Bienne, Saint-Imier, and Le Locle.

Given its Swiss heritage, COSC only certifies timepieces manufactured in Switzerland. Many luxury watch brands, such as Rolex, Omega, and Breitling, regularly send their watches for testing and certification. Watches made outside Switzerland follow their own precision standards. For instance, German watches use the DIN 8319 standards and are tested at the Glashütte Observatory, while Japanese chronometers usually undergo in-house testing.

What Does the COSC Testing Process Involve?

The COSC certification process is not for the faint of heart – or rather, the faint of tick. Each uncased movement is rigorously tested for 15 consecutive days. The movements are assessed in five positions and at three different temperatures (8°, 23°, and 38°C), with the mechanisms left at the specific temperature for 24 hours in a designated position.

Afterward, these watches are photographed to gauge their performance and precision. These tests culminate in an analysis of seven different criteria:

  1. Average daily rate
  2. Mean variation in rates
  3. Greatest variation in rates
  4. The difference between rates in horizontal and vertical positions
  5. Largest variation in rates
  6. Variation in rate depending on temperature
  7. Rate resumption

Only when a watch satisfies all these benchmarks is it awarded the coveted COSC certificate.

The COSC Legacy

Spotting ‘COSC Certified’ or ‘Superlative Chronometer Officially Certified’ on a watch dial isn’t just a fancy addition. It’s a testimony to the precision, reliability, and exceptional quality of the timepiece. A COSC certified watch is a symbol of fine craftsmanship, a testament to the rigorous standards of Swiss horology.

So, the next time you see a COSC certification on a wristwatch, remember the rigorous testing and dedication to precision that it represents. The COSC certification is more than just a term to distinguish Swiss watches; it’s a recognition of the crème de la crème of Swiss watchmaking.

COSC watches on offer at Sekvens

Both Squale and Ollech & Wajs offer COSC certified models, these will stay accurate for many years to come.

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