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I recently learned that mechanical watches becoming magnetized is "a real thing". My friend has a Girard Perregaux Ferrari watch, which uses an ETA 2892 movement with a stopwatch complication. For watch porn, it looks like this:
View attachment 120074
The local watch guy wanted some ridiculous sum to regulate it, so I did it for him. It ran reliably just much too slow. It was clean inside, didn't seem to need disassembly or lubrication so I simply adjusted the beat and speed. The 2892 has a fine-adjust for speed regulation which is a very nice touch - I wish the Miyota 9015 had that! Got beat to 0.0 to 0.2 ms across all positions and speed at +/- 2 sec per day. Face up (fastest position) at +2 and crown up (slowest position) at -2. It was running great for a few weeks. Then suddenly it started running fast 45-60 seconds per day.
I held it near a compass to test and it would swing the compass almost 180 degrees! I have an old wand-style tape deck demagnetizer, so I used it on this watch, slowly swirling around the case front & back and smoothly slowly pulling it away. Got it to where it doesn't move the compass more than 5 degrees. And, the speed went back to its old +/- 2 sec per day.
What was the magnetizing culprit? His microwave oven!
Lessons learned:
- Mechanical watches can and do get magnetized, and it does affect their regulation.
- Microwave ovens (and perhaps other household appliances) have powerful magnets that can magnetize watches.
- You can demagnetize a watch with any old wand-style tape deck demagnetizer.
And here's the machine used back in the day to de-magnetize!