A watch that suddenly gains two, five or ten minutes a day is almost never broken: it is magnetised. This is the most common fault and the easiest to correct — provided you recognise it and use the right method.
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 amplitude collapse, an erratic positional rate, or 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. Alternative: a sewing needle floated on water and pulled towards the case. These tests catch 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. A properly demagnetised watch recovers its original rate immediately.
Avoiding a relapse
The sources are no longer airport gates but everyday objects: magnetic bag and case closures, magnetic phone mounts, earphones and speakers, induction hobs, 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.
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.