Source: Omega, Tissot, Bremont, Ball Watch via Bloomberg

What Is a Chronometer? A Guide to These Top-Notch Watches

And which one should you buy?

The watch world is full of jargon that's tough to understand. Chronometer might sound like a mouthful, but it's just a fancy word for "really, really precise watch."

The word chronometer goes back to the early eighteenth century, when an English clockmaker called Jeremy Thacker invented a vacuum-sealed clock. Without air resistance, it was extremely accurate; Thacker dubbed his creation a chronometer. The name was later used a few decades later to describe marine chronometers—clocks suspended in gyroscopic boxes that helped ships determine longitude and traverse the world's oceans. Today you can wear their precision-crazed successors on your wrist.

As with most things in the Swiss watch industry, the term "chronometer" is closely guarded. A watch must pass through the Contrôle Officiel Suisse des Chronomètres (COSC) in order to carry the term on its dial. The COSC, a testing institute, subjects a watch's movement to a multi-day examination that places it in five different orientations and three different temperatures to gauge its precision amid varied conditions. The final result must be a daily variation no more than -4 or +6 seconds per day for a mechanical movement. (There are standards for battery-powered watches, too, though very few brands produce them.) Only 3 percent of watches produced in Switzerland make their way through COSC's certification process; some equally precise watches are not submitted for testing.

A lot of factors can contribute to a watch making it through COSC's grueling tests (or failing, for that matter), but two qualities must be present for a watchmaker's work to qualify as a chronometer: good materials and high quality control. Better metal alloys and such materials as silicium are less susceptible to expanding and contracting when the temperature changes. Nor are they as easily degraded by friction. When you're relying on a steadily beating spring and some gears to keep time, this is paramount. And even if you have the best raw components, they need to be assembled properly to function at their peak. Pinions need to be well-oiled, gears precisely cut, and everything locked together nicely and tightly.

Whether you're new to chronometers or have a collection of always-on-time watches, here are a few to look out for.

Tissot Le Locle

The Le Locle is a super-precise watch that punches far above its price bracket.
The Le Locle is a super-precise watch that punches far above its price bracket.
Source: Tissot via Bloomberg

You don't have to spend a small fortune to get something mechanically reliable. Tissot makes a few chronometers with three-figure price tags, but you should spend just a little more to spring for the Le Locle. It has a souped-up automatic movement that won a national chronometer competition when it was first released in 2012, beating out watches that cost more than 10 times as much. $1,295

Ball Trainmaster Standard Time

Ball stuck with tradition for this throwback to the original railroad pocket watches.
Ball stuck with tradition for this throwback to the original railroad pocket watches.
Source: Ball Watch via Bloomberg

Just as marine chronometers pushed exploration by ship, accurate pocket watches made it possible to standardize time across the U.S. railroad system. Ball pioneered these pocket watches back in the 1800s and is still making wristwatches in the original style. The Trainmaster Standard Time has an enamel dial and bright luminous markers that are actually tiny, gas-filled tubes for maximum glow. $7,699

Bremont MBIII

Built like a tank, the MBIII maintains precision through anything you can throw at it.
Built like a tank, the MBIII maintains precision through anything you can throw at it.
Source: Bremont via Bloomberg

The British brand might not be subject to the Swiss chronometer regulations (nor do most of their watches say chronometer on the dial), but almost every watch in its lineup is COSC-certified. The MBIII is an evolution of Bremont's signature watch, inspired by a famous fighter-jet ejection seat. It adds a second time zone hand to the mix, while still being easy to read—and nearly indestructible. $6,395

Omega Globemaster

The Globemaster is the first watch to bear a new certification, Master Chronometer.
The Globemaster is the first watch to bear a new certification, Master Chronometer.
Source: Omega via Bloomberg

Omega's upping the ante with the Globemaster, introducing an even more stringent grade of certification, the Master Chronometer. Not only does this watch go through the usual temperature and movement tests, but it is tested in strong magnetic fields—something that's increasingly practical because everything, from your cell phone to your refrigerator, contains magnets these days. Way to ruin it for everyone else, Omega. From $7,700

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