One day my kid slapped a magnet on my mechanical watch (Seiko Orange Monster SKX781). After that it ran very fast like a minute or two per day.

Bought a cheap demagnetizer off eBay and used a simple compass to show if the watch was magnetized or not.

For more info and comments, follow the link below.

http://jikanwatch.blogspot.com/2012/04/do-it-yourself-diy-mechanical-watch.html