Demagnetization

[Fitron]

I've just started a new job in a pulic library and there is a security system in place to prevent theft. Each item has a metal strip which is remagnitized on return and demagged when issued. I'm told that this can make your watch run slow but can anyone explain why - and could this prove dangerous to digitals? - no one there knows about my interest in watches so I don't think this is a wind up. Anyone got any ideas ?

[rewolf]

AFAIK it's only dangerous for mechanical watches. If the spring gets magnetized, its windings will stick together so it can't work properly.

I remember as a child my very first watch was mechanical. On the back it read "antimagnetic". I wanted to know if this was true an tried it with a strong magnet. The watch WAS attracted by the magnet - I was disappointed. Only minutes after, the watch stopped.
Luckily my grandpa was a hobby watchmaker (he had given me this watch as a gift only a few days before) and he had a demagnetizer. He showed me the magentized spring and explained what had happened. I don't remember though what that "antimagnetic" actually meant.

[Fitron]

Hmm does that mean that should it be demagnitized by the "clunker" for letting the books out of the library and the only real potential problem is remagnitzing when checking them in....

[Planet-LED]

Fitron,

You are going to have to be careful if you have any LED watches that use magnets and reed switches. You wouldn't want those watches anywhere near that demagnetization equipment.

[Fitron]

You wouldn't want those watches anywhere near that equipment.

Score! I can buy some more jumps and (whispers) analogues. Seriously though I think you're spot on. The P2 and TC1 stay at home. My others are possibles. Hmmm perhaps the witts as the hughes is relatively easily replacable. If anything happens I'll be sure to post it. Thanks all.

[azimuth_pl]

go ahead Campbell, I've got a demagnetizer
the system you're describing is also used in supermarkets at the cashdesk conveyor. it demagnetizes those chips so it's also not a good idea to place your creditcards on the conveyor when paying. however the magnetic charge is not that strong to kill a watch.
nowadays all mechanicals are antimagnetic against standard magnetic fields for a short period of time, even the balance spring. however a very strong magnet can magnetize even "antimagnetic" metal parts