In Short: COSC Certification
Here’s a term you may hear tossed around if you spend any time on our blog: COSC certified chronometer. What’s any of that mean to you? Well, if you’re a person that prides yourself on being prompt, courteous, and timely, it should mean quite a bit to you. If you rely on your watch to maintain your schedule throughout the day (pulling a phone out of your pocket is so unbecoming), then having a COSC certified chronometer should mean a whole lot to you. The word certified is easy enough, but let’s a closer look at the other two: COSC and chronometer.
COSC stands for Contrôle Officiel Suisse des Chronomètres, and they are the official Swiss chronometer testing institute. Uncased movements looking to gain chronometer status must pass a series of tests to verify accuracy to within an average of -4/+6 seconds a day. This means the watch can not lose more than 4 seconds, or gain more than seconds of time each day. To get this average, the movement is tested for 15 days, in 5 different positions, and at 3 different temperatures. While only 3% of Swiss watch production is COSC certified, the brands that do go through the trouble of gaining official chronometer status, often stay well within the -4/+6 second guidelines.
Movements that gain COSC chronometer certification are free to label the achievement on the dial of the watch they are destined to live within. Inspect the dial of the Rolex above and you’ll notice the words Superlative Chronometer Officially Certified at 6 o’clock. What that boils down to is this: the watch is going to be accurate enough to keep you on time throughout the day, unless things like timing the half-life of Hydrogen-7 fall within your normal daily activities.
The topic of chronometers is a deep rabbit hole, and there are even competitions that revolve around achieving the most accurate mechanical movement. That’s a story for another day. Until then, check out a selection of certified chronometers available on StockX right now.
The low Ask on this Planet Ocean currently sits at $4,050. Not only is the movement chronometer spec, it’s built by Omega. Plus it’s got a ceramic bezel. This is a steal, Bid on it here.
This Submariner, along with every other Sub available on StockX, is what Rolex calls a Superlative Chronometer. Rolex tests their movements to better than the standards set forth by COSC, which is why they add the word Superlative to the dial. This LV Sub has a low Ask of $8,300, snatch it up right here.
The Tudor North Flag is a bullet-proof (not really, don’t test that one) tool watch with a bare bones, Tudor-built movement that also happens to be a certified chronometer. Get this example at under $3,000 right here.
This Ulysse Nardin is a practical example of formal wear thanks to its chronometer grade automatic movement. This watch has a current low Ask of $6,600 right here.