Time on: watches you can set your watch by

Just what is a chronometer? And how accurate is a mechanical watch?

It’s one of the most common mistakes made by consumers when trying to get their heads around watch jargon – muddling a chronograph with a chronometer. The former, as the Greeks would have it, is a ‘time writer’, a device that can capture the timing of a single event. So a stopwatch for fancy people. The latter is a watch powered by a movement that has been independently certified for accuracy by some of the most pedantic people in the world – the boffins at the Contrôle Officiel Suisse des Chronomètres, or COSC for short.

These guys are pretty fastidious. They take movements, uncased and usually supplied by brands, and then test them for 15 days in five different positions and in a range of temperatures, measuring them for accuracy as they go. If at the end of said test they are, on average, accurate to within -4 to +6 seconds a day, they are deemed worthy of chronometer status.

What does this mean? Depends on who you ask. While around 6 per cent of watches leaving Switzerland carry the chronometer designation, these days, a lot of companies make watches with movements accurate enough to be chronometer-certified, but don’t bother getting them tested, either because they want to keep the cost down – on a mid-range watch, you can expect to pay circa £200 extra for a watch with the word chronometer on the dial over a standard mechanical – or, more likely, because they don’t think the standard is tight or exclusive enough. Patek Philippe, for example, self-certifies with the Patek Philippe Seal, which assures buyers of accuracy to -3 to +2 seconds a day. 

Others are more convinced. Most Rolex watches are chronometer-certified, although the company would like you to know that its in-house suite of calibres includes units such as the 3235, which, it says, is accurate to -2 to +2 seconds a day, after casing. Omega is another fan, although it now qualifies its watches as ‘Master Chronometers’ to certify that not only have they been through COSC, they’ve also been ok-ed by METAS, another independent organisation that guarantees Omega’s movements retain their chronometer-level performance even when cased and submitted to a barrage of tests for things such as anti-magnetism.

Ultimately, what you get with chronometer status is an extra degree of reassurance that your watch is at least going to keep you vaguely on time, and a bit more Swissness on your wrist. The Swiss boast of superlative accuracy is generally over-egged, or at least anachronistic – a mechanical watch can’t compete with a solid battery-powered quartz on that front, and certainly not a GPS-enabled smartwatch.

But then let’s allow ourselves to marvel at a mechanical object that beats at 28,800vph and can do that accurately to within seconds a day. And besides, why would you want a watch any more accurate? Life is exacting enough as it is.

The big players in the world of chronometers are Rolex, Omega and Breitling, with a supporting cast of around 60 brands each year, including Chopard, Panerai, TAG Heuer and Tissot. Although for now, details of how many of each pass the test are no longer available. As of last year, COSC stopped reporting a brand-by-brand breakdown (watch nerds are up in arms…).

Here are five chronometers to set your watch – and your life – by.