Two independent standards for watchmaking accuracy.

There is a well-founded expectation that your watch should be accurate. After all, the main reason these instruments exist is to tell us what time it is, not what time it isn’t. Mechanical watches’ accuracy can depend on how well the springs and gears are made, and how the watch deals with shock protection, magnetism, temperature, and even gravity. An inexpensive watch can be off by as much as a minute a day; a well-made one can be within a second or two of being perfectly accurate every day.


The question is, how do you know how accurate a watch is when you purchase it? Many companies use internal standards to reflect the testing they say has been done to the watch: Patek Philippe has the Patek Seal, Rolex calls their watches Superlative Chronometers, and Jaeger-LeCoultre’s Master Collection goes through 1,000 hours of testing. The problem with this kind of testing is that they are held to a standard that is not subject to anyone else’s review. On the other hand, third-party testing is purely about the performance of the watch, no matter what the brand is or what the marketing materials say. This is where COSC and METAS enter the conversation.


What is COSC?

COSC stands for Contrôle Officiel Suisse des Chronomètres. It is a non-profit organization that was founded in 1973 to ensure a standard of accuracy across the Swiss watch industry. This testing institute will take any movement that is submitted to any subject through fifteen days of testing. During that time, the movement will be put into five different positions and three different temperatures of 46°F, 73°F, and 100°F. When tested, the temperature should not affect the watch more than .6 Seconds a day, and the average daily rate cannot be more than -4/+6 seconds off.

Watch on a Timegraph


If a movement passes these tests, it becomes chronometer certified. Overall, only about 6% of Swiss watches meet these certifications, and its proof of a well-made movement. Some brands, like Breitling (since 2000), certify every watch they sell as COSC chronometers.

Breitling with Chronmetre on the dial, this means it is COSC certified


What is METAS

METAS is a Swiss government science agency that translates to the Federal Institute of Meteorology. In 2015 the Swatch group worked with the Swiss government to create a new third-party test. The focus was on certifying watches that are fully cased rather than just the movement, and to add testing for anti-magnetism to help watches survive in the modern world of electronics.

The Master Chronometer on the dial means this OMEGA is METAS certified


The watch is tested in six different positions and must maintain an accuracy of -0/+5 seconds a day while they are subjected to temperatures of 73°F and 91°F. The watches must also match the stated power reserve and water resistance. The biggest challenge is magnetic exposure testing. The watch will be exposed to 15,000 gauss, or about the same magnetism as an MRI machine. Even watches that are traditionally referred to as anti-magnetic are only built to withstand 1,000 gauss before magnetism starts to affect them. The exposure to magnets can magnetize a watch, making the springs and gears become attracted or repulsed by each other, which throws the delicate dance of timekeeping into disarray.

Chamber watches are subjected to 15k Gauss for METAS testing

If a watch passes all these tests, they are considered Master Chronometers. Originally OMEGA was the first to have their watches tested to METAS standards, slowly making almost all their watches Master Chronometers. Recently Tudor has followed suit and began testing some models to meet the new METAS certification.


Watches about to be water pressure tested at METAS

Both certifications are proudly worn on the dial of the watches that earn them. They show a commitment by the watchmaker to produce well-made and highly accurate timepieces. If the watch you are looking to purchase has either a Chronometer or Master Chronometer on the dial, it has passed the test – and deserves a good home.


To find the chronometer of your dreams head over to Crown and Caliber.

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Crown & Caliber is the smartest way to buy or sell a luxury watch. As an exclusively online marketplace for pre-owned timepieces, Crown & Caliber exists to ensure that when it comes down to the final transaction, buyers and sellers can both win. For sellers, we do all the legwork of valuating, marketing, and selling—for buyers, we put trust back into the act of purchasing sight-unseen with our servicing and authentication process. By emphasizing transparency and placing value on quality, Crown & Caliber has become the preferred marketplace for watch collectors and casual enthusiasts alike.

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