Why does a magnet make your watch run fast? The video guide

Chapters

1. 0:00Running fast for no reason
2. 0:15The hairspring gets magnetised
3. 0:33The coils stick together
4. 0:47Magnets everywhere
5. 1:05The ISO 764 threshold
6. 1:22Two centimetres are enough
7. 1:44What about quartz?
8. 2:03Nothing is broken

Transcript

Has your mechanical watch suddenly started running fast, with no knock and no obvious reason? The culprit may be invisible: a magnet. At the heart of the movement, the hairspring, that spring as fine as a hair, is often made of a steel alloy. Brought close to a magnet, it becomes magnetised itself, and stays that way once moved away. Its coils then stick to one another. The spring behaves as if it were shorter: the balance beats faster, and the watch gains time. In severe cases, it stops. Magnets are everywhere: bag clasps, phone cases, speakers, tablets, laptops. At contact, the magnet in a tablet connector can exceed the threshold of the anti-magnetic standard ten times over. That threshold is the ISO seven sixty-four standard: four thousand eight hundred amperes per metre. The watch must not stop during the test, nor drift afterwards by more than thirty seconds a day. The good news: the field drops very quickly with distance. In a study published in twenty twenty-five, less than two centimetres from the devices tested, it had already fallen well below that threshold. Put your watch next to the bag, not against the clasp. A quartz watch reacts differently. Its little motor works with a magnet: a strong field can stop it or upset it while the exposure lasts. Once moved away, it gets its accuracy back: you simply set the time again. For a magnetised mechanical watch, nothing is broken: the hairspring is not damaged, only magnetised. A watchmaker demagnetises it in a few minutes, without opening the watch, and the coils separate again. Discover a whole selection of watches at Montres Outlet.