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How do they work?
Magnetic fields are one of the most common factors negatively affecting the accuracy of a mechanical watch. Metal internal watch parts can become magnetized when introduced to these fields. The most common target is the balance spring: the long, curled-up strip of metal that oscillates in conjunction with the balance wheel, regulating the ticking of a watch. When the balance spring becomes magnetized it sticks to itself, effectively becoming shorter, which causes the watch to oscillate faster, thus causing the watch to run fast. That’s the most common problem, anyway; exposure to magnetism can also interfere with the balance spring’s temperature compensation, causing the watch to run at different rates in different temperatures.
Watchmakers have devised two different ways to battle magnetism. One is to protect the entire movement with an inner cage made out of a very magnetically permeable material, usually soft iron, that attracts the magnetic field lines, leaving the movement itself unaffected. Soft iron is easily magnetized, but unlike some materials (like steel), it doesn’t remain magnetized once the source of the magnetic field is no longer present.
The other method is to make balance springs and other parts from nonferrous materials that aren’t easily magnetized. Historically, steel has been a common balance spring material, but for the last several decades, Nivorox (a nickel-iron alloy) and similar alloys have been industry go-to’s, partially due to their improved magnetic resistance (but not imperviousness). More recently, watchmakers have been making balance springs from silicon, which has generally proven to be a far more effective solution.
Where did they come from?
Vacheron Constantin is credited as the first watchmaker to attempt making an antimagnetic watch, having done so in 1846 with a palladium balance sprin. The company wouldn’t successfully build an antimagnetic watch until decades later, when it eventually made the world’s first antimagnetic pocket watch in 1915. Tissot created the Antimagnétique in 1930, supposedly the world’s first antimagnetic wrist watch.
Antimagnetic watches didn’t really enter the mainstream until a couple decades later. A notable boon to the development of antimagnetic watches was the creation of the Jaeger-LeCoultre and IWC Mark XI-spec watches in 1948, created at the behest of the British Ministry of Defense, which, among other requirements, demanded its pilot watches to be antimagnetic. Not long after Rolex created the Milgauss at the request of the CERN, and Omega and IWC also made their own antimagnetic watches for other professionals who worked in the presence of strong magnetic fields.
Why does it matter?
The antimagnetic watch, or at least antimagnetic advancements, remain fairly relevant today. In the ’40s and ’50s antimagnetic watches really only proved essential to engineers, scientists and other professionals who encountered strong magnetic fields on a regular basis, but think about all the electronic devices that surround us today: Smartphones, computers, tablets, monitors, speakers, kitchen appliances — they all produce magnetic fields and all have the potential to mess with your watch’s accuracy.
How much protection you need, though, is a different story. The magnetic field produced by a microwave oven from an inch away, for example, is only about two gauss. Power tools, from the same distance, will produce up to about eight to ten gauss. So yeah, something like Omega’s 15,000+ gauss-resistant Aqua Terra or Rolex’s Milgauss (1,000 gauss resistant) is overkill for regular wear. That said, demagnetization is a fairly common watch servicing requirement, so while the fix is cheap and easy, if you’d rather avoid having to take a watch in for service altogether, an ISO 764 compliant watch — which is resistant to magnetic fields up to 4,800 A/m, or about 60 gauss — should be plenty. Still, like super-deep dive watches or ultra-complex movements, embracing the overkill is all part of the allure.
Who does it best?