A watch that suddenly gains two, five or ten minutes a day may be magnetised. It is the hypothesis to test first, because it is easy to correct — but it is not the only one: a shock, stuck or distorted hairspring coils, a damaged regulating organ or an escapement fault produce similar symptoms. If the rate does not recover after demagnetising, the cause lies elsewhere.
Typical symptoms
The most characteristic sign is a sudden, large gain that appeared overnight, without a shock or a fall. The hairspring coils stick together, the active length shortens, the frequency rises. Depending on severity you may also see an erratic rate, or even an outright stop. A watch that has been losing gradually for months is a maintenance matter, not magnetism.
The home test, in thirty seconds
Slowly bring a small compass (a smartphone compass app works if the sensor is decent) near the case, then rotate the watch. If the needle clearly deflects and follows the watch, the movement is magnetised. This test catches strong magnetisation, not weak residual fields — only a timegrapher reading before and after demagnetising settles it.
Demagnetising properly
A workshop demagnetiser creates a decaying alternating field: press the button, pass the watch over the plate, then withdraw the watch slowly — several tens of centimetres — before releasing the button. It is the gradual withdrawal inside the field that demagnetises; releasing the button with the watch still on the plate can re-magnetise it. Repeat two or three times in different orientations, then re-check the rate.
Avoiding a relapse
The usual sources are everyday objects: magnetic bag and case closures, magnetic phone mounts, earphones and speakers, magnetised tools, tablet covers. Store the watch away from these, and remember that a silicon or antimagnetic hairspring (Parachrom type) greatly reduces the problem without removing it, since other steel parts remain sensitive.
Standards and modern solutions
The reference framework is the ISO 764 standard: a watch called antimagnetic must withstand a field of 4,800 A/m (about 60 gauss) with a tolerated rate deviation of ±30 s/d. Far beyond that, the Master Chronometer label of METAS (the Swiss Federal Institute of Metrology) requires resistance to 15,000 gauss. Three defences coexist today: the silicon hairspring, non-magnetic by nature; Rolex's Parachrom hairspring, made of a niobium-zirconium alloy; and, an older solution still in use, the soft-iron inner case that channels the field around the movement like a Faraday cage.
Frequently asked questions
Can demagnetising damage the watch?
Not a mechanical movement. Avoid exposing a quartz watch or an electronic module to a powerful demagnetiser.
Does the case have to be opened?
No: the field passes through steel and sapphire. Demagnetise the watch closed, bracelet included.
My watch still gains after demagnetising — why?
Either magnetisation persists (repeat, varying the orientation), or the cause lies elsewhere: regulator setting, touching coils, or a distorted hairspring. A timegrapher reading decides.
Want to test all this at the bench? The Décalibre laboratory devotes a full module to magnetism, with an everyday-object scanner and a simulated demagnetiser.