See full version: Chronometer: How Important is Accuracy for a Mechanical Watch
The deviation is so small that you could say it’s like sailing from London to New York and only missing the full stretch by a couple of inches. Watchmakers over the years have tried to negate such deviations with pioneering inventions such as tourbillon movements and even more recently co-axial movements, but the fact remains that there are still deviations.
They say time waits for no man but there is an exception to this saying. You see, mechanical watches have long been a sought after male accessory, even to a point where it is no longer an accessory but moreover an item of infatuation that is collected by many. However, for those who don’t quite understand or can at least sympathise with this habit, see it as more of a strange obsession. Why? Well for them, and quite understandably too, mechanical watches just aren’t as accessible as quartz watches – which isn’t explicitly true – but there is rather another interesting factor to why some also consider mechanical watches to be, well, just not that great minus the fact they tend to have quite lofty price tags attached to them: they are just not as accurate as one would expect.
Since the dawn of watches every watchmaker has long strived to reach perfection, with the utmost target being accuracy. But while watchmakers will make sure the timepieces they produce are as accurate as can be, by using a Witschi (an instrument to test the precision of mechanical movements), there are still daily deviations. Then you’ve got mechanical watches that sport what is called an “officially certified chronometer” movement, which is controlled by Contrôle Officiel Suisse des Chronomètres or COSC for short. What exactly does this mean? COSC (a non-profit organisation) was setup to test the accuracy of movements and have a certain set of rules that need to be adhered to when certifying any mechanical watch movement manufactured or assembled in Switzerland.
Each uncased movement submitted by any brand is individually tested over a period of fifteen days, in five different positions, at three different temperatures. Over the duration of this test there must not be a larger deviation than between -4 or +6 seconds a day, though some may consider this to not even be accurate enough. What one must remember is that there are 86.400 seconds in a day! here
Though, make no mistake that even some movements made by the Germans, the Japanese, and even the Swiss that haven’t been certified actually surpass the COSC requirements.
Not to be confused with a chronograph, a chronometer is a watch that has been tested and certified to be incredibly accurate by some sort of governing body. The most prominent example of that today is the Official Swiss Chronometer Testing Institute (COSC), which is responsible for testing Swiss-made chronometers; only the COSC can deem a Swiss watch worthy of “chronometer” status, though other countries have their own chronometer testing outlets, like the Glashütte Observatory in Germany. While quartz watches can also be certified as chronometers, the term most often refers to certified mechanical watches that are accurate to within just a few seconds per day (as an example, COSC-certified chronometers must accurate to within -4/+6 seconds a day). Some brands, like Rolex and Omega, do their own, more stringent, certification programs in addition to COSC testing.
Aside from having to readjust your watch less often, there’s not much of an argument to be made, practically speaking. Marine chronometers were cutting edge in their day, but timekeeping has progressed to the point where cheap quartz watches and atomic clock–regulated smartphone clocks are far, far more accurate. Given this, nobody really buys a COSC watch because they need it to be accurate — considering that only about six percent of Swiss watches produced are COSC certified, it’s mostly for the bragging rights. [links]
The watch world is full of highly technical, often highly French terms that any normal person, reasonably, doesn’t know. Welcome, then, to Horology in a Hurry, a semi-regular column where we’ll break down these terms at length one at a time to give you a better understanding of how watches work. This week: Chronometer. more
Though you could make the argument that chronometer-grade movements are just better quality than other mechanical watches — for example, COSC-versions of ETA movements use upgraded shock-protection systems, hairsprings and mainsprings compared to their standard-grade counterparts. And given that watches that pass the COSC’s testing keep accurate time when subject to mechanical shocks and temperature variations, a case could be made for durability, too. But at the end of the day, in terms of watch nerdery, there’s certainly something impressive about having an antiquated piece of machinery keep particularly accurate time and the watchmaking skill it takes to make it possible.
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One of the criteria for « chronometer » certification is the average daily rate on the first 10 days of testing: from -4 sec to +6 sec., or up to 10 seconds per day. A tolerance which, as such, may appear high, but which, in reality, is the result of an extraordinary requirement.
Because it also represents the recognition for the brand of a flawless quality system – the proof that the notion "chronometer" has informed its every level of production: research and development, design, production, choice of components and of partners, assembly, adjustment, control, with a constant concern for the criteria that define a true chronometer. The failure rate among major brands is extremely low compared to the volume submitted, which is proof of the rigour of the brands in question.
A well-built watch consists of over a hundred moving parts, all machined with an exacting level of precision. Some of these parts are extremely small, which means that a very small change in size of any of those parts can become magnified as the watch movement works. here
The timegrapher is a very specialized device that can measure the accuracy rate of a watch almost immediately. The tool has a small pedestal to hold your watch; once your watch is in place and the device is activated, it will tell you the accuracy of the movement inside the watch in seconds instead of days. [links]
There are extremely accurate timepieces, for example an atomic clock, that keep time by measuring the vibrational frequency of an element, but even these are not perfectly accurate forever.
Many of those tiny, precision-machined parts inside your watch are made from ferrous metals, which means they are affected by any magnetic field they’re exposed to. here
For a mechanical watch movement, there are seven different things that are measured to determine its accuracy: