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The Controle Officiel Suisse de Chronometres is the official accuracy and precision testing organization of both mechanical and quartz Swiss-made watches.
Founded in 1973, the COSC institute is a non profit organization set up to measure the accuracy of watches and no doubt give Swiss watchmakers a bit more credibility than rival foreign brands. Before COSC was founded, Swiss watches were still tested for accuracy, although these requirements were a little less strict, allowing +1/-10 seconds, with tests taking place all around the country, not one specific location.
Surprisingly, only 3% of watches made in Switzerland receive the official chronometer stamp of approval. It is not known whether these watches do not meet the standards required, or whether brands simply do not care enough to test them.
A full list of COSC specs required are shown below which show the exact definition of both swiss quartz chronometer and swiss mechanical chronometer standard watches.
Table of Contents
What Is A COSC Certified Watch?
A COSC certified watch means that the movement used has passed a test of strict criteria shown below. This test is different for both mechanical and quartz watches. If this test has been passed, then the brand is allowed to print “chronometer officially certified” on the dial of their watch.
To ensure accuracy, watches are tested against atomic clocks. The most accurate atomic clock is currently does not lose or gain 1 second per 20 million years.
Mechanical Requirements
- 15 days of testing
- Variation allowed per day +4/-6 seconds
- Mean variation allowed, 2 seconds
- Biggest variation allowed between testing each day, 5 seconds
- Thermal variation of +/- 0.60 seconds
Quartz Requirements
- 13 days of testing
- Watches are tested at 3 different temperatures and 4 variations of humidity
- Variation of +/- 0.07 seconds at 23c
- Variation of +/- 0.20 seconds at 8c
- Variation of +/- 0.20 seconds at 38c
- Humidity variation of no more than +/- 0.10 seconds
Which Watch Brands Have The Most COSC Certified Watches?
COSC no longer publishes figures to protect brand confidentiality, so it is not known who has the most COSC certified watches.
This is a very strange decision as by not knowing who produces most chronometer standard watches, it is difficult to see who the up and coming brands are, as well as anyone whose production quality may have declined.
In 2015 (which was the last year results were printed), these were the results:
- Rolex – 795 716
- Omega – 511 816
- Breitling – 147 917
- Tissot – 96 563
- Mido – 49 962
The difficulty in interpreting this data is that companies with larger production facilities will no doubt have more watches that meet requirements. As an example, Titoni and Christopher Ward have 4146 and 3362 watches which meet the criteria respectively. However, we have no real idea how many more Omega watches are produced than these brands, which makes an accurate judgment even more difficult.
How Do I Know If A Watch Is COSC Certified?
As being COSC certified is a badge of honor for the watch movement. Officially certified watches will print “chronometer officially certified” on the dial. Much like being “Swiss made” you are not allowed to print this if it is not true (although there are some Chinese brands who have been caught breaking the rules).
Although COSC certified watches come with a certificate for the manufacturer, brands such as Rolex will not supply this paperwork to customers. One reason for this may be that the average customer has no idea what COSC standards are, therefore raising more questions than answers. Another reason is that when purchasing a watch, you’re mostly buying because of brand and style. If people considered Mido and Rolex movements to be very similar, they may change brand allegiance.
Is Certified Chronometer The Same As COSC?
COSC is the organization that awards certificates for movements that meet its criteria. Therefore, watches that state “chronometer officially certified” have all been verified by COSC.
The only exception to this is when a poor quality brand tries to pull the wool over your eyes. As previously mentioned, some Chinese brands have printed “certified chronometer” when they are using a very basic Sea-Gull movement. Apart from this though, a reputable Swiss brand would never lie about being COSC certified.
Are All ETA Movements COSC Certified?
No, in fact even the same model of movement can both pass and fail COSC requirements depending on the adjustments that have been made to it. This excellent blog post shows that there are 4 grades within the ETA caliber 2824-2 alone, proving that there can be a massive difference between the top and bottom range of a standalone movement.
Obviously, there are also ETA movements significantly worse than the 2824-2 which will not be sent for COSC certification.
What Is The Cheapest COSC Certified Watch?
As prices are always changing, it can be difficult putting a name to the cheapest COSC certified watch.
With that being said, there are some strong contenders listed below, which must be in the region of the cheapest chronometer watches money can buy. Remember, not every model is the same and you must look for the text on the dial confirming that the watch is in fact built to chronometer standard.
Generally, you’re going to struggle to find anything sub $600, although when on sale, it is possible. As a general rule, the brands you should be looking at are Tissot, Mido and Christopher Ward, any other brands are a lot more expensive than these three.
Tissot Ballade
Mido
Is COSC Certifcation A Good Measure Of Reliability?
There is no doubt that COSC measures the accuracy of quartz and mechanical movements very well. The test, although not perfect, is fairly exhaustive and uses a variety of ways to look at a movement, rather than one single measure. However, this does not mean that COSC certification is without fault.
The Main Issues With COSC
The first glaring point is that COSC only tests Swiss made watches, there are no COSC certified Japanese watch brands, nor German or any other watchmaking country. This may sound irrelevant, but what is the point of having an accuracy test, if you cannot compare different companies?
Excluded top brands include the likes of A Lange und Sohne, Nomos, Grand Seiko and Bremont. So if we are to take a well known chronometer standard watch such as the Omega Seamaster, it cannot be compared with a Grand Seiko unless you were to run the test yourself. This is a pretty poor situation and a prime example of Swiss protectionism within the watch industry.
Secondly, brands such as Rolex still have their watches COSC certified, but have much higher internal testing requirements using -1/+5 rather than -4/+6. This shows that a COSC certificate is more of a way to market and sell a watch than anything meaningful.
Lastly, complications are not tested. If a luxury watch has a chronograph, moonphase or tourbillon, there is no real way to tell if this is any more than decoration. If a tourbillon made no real difference to the accuracy of an already accurate movement, you would be hard pressed to know this without running lab tests yourself. The same can be said for moonphase indicators and chronographs. If these instruments were running slightly out of sync, it’s likely you would never find out.
In summary, the accuracy of movements is something that is often bought up and compared, but complications may be far better in one brand compared to another. Until there is a measurement for these things it is difficult to say one company is superior to another.
