Watch Magnetism Explained: Why Your Watch Runs Fast and How to Fix It

If a mechanical watch suddenly runs several minutes fast or slow in a day, magnetism is a common cause. It is annoying but usually easy to fix.

The hairspring, which controls the balance wheel, is the most sensitive part. When it becomes magnetised, the coils can stick together slightly, which shortens the effective spring and makes the watch run fast. Other steel parts can be affected too.

Everyday magnets are everywhere: speakers, tablet cases, magnetic bag clasps, fridge doors, laptops and phone chargers. Most are weak, but regular close contact can add up. Keep your watch a few centimetres away from them when you are not wearing it.

To check, many watchmakers use a demagnetiser, which is a quick and inexpensive job. You can also buy a small demagnetiser or use a compass: if the needle swings when you bring the watch near, the watch is probably magnetised.

Some watches are built to resist magnetic fields, using a soft iron inner case or non-magnetic parts such as silicon hairsprings. Brands list this as anti-magnetic resistance, but check the claim, as the level of protection varies widely.

Quartz watches are largely unaffected, because the quartz mechanism does not rely on a hairspring, though a very strong magnet can still affect the stepper motor. If your mechanical watch gains time suddenly, try keeping it away from magnets for a day before you worry about service.