Magnetization
Also called magnetized, magnetised
Magnetization is when parts of a mechanical movement, most often the hairspring, become magnetised by exposure to magnets in everyday objects, causing the watch to run erratically, usually much faster.
It's one of the most common reasons a well-running watch suddenly misbehaves, and it's usually fixed quickly and cheaply by demagnetising, without a full service.
If a watch you're buying runs very fast, check for magnetization before assuming it needs a service.
A simple compass placed near the watch can hint at magnetization, and a demagnetiser is a cheap tool that many dealers keep for exactly this reason.
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