OMG Christofle! I had no idea about this. I have been told this repeatedly, have three right now & love them. I'll be talking to the guys I got my watches from about this. Thanks for the info.
This might be valuable information for you!
A watch can be considered anti-magnetic if it can run within a 30 seconds per day deviation while housed inside a magnetic field of 4,800 A/m. And while that sounds like a lot, consider that even a small magnet, like those found in your iPad cover, stereo speakers or computer monitor, can be enough to throw your fine timepiece out of whack by causing the hairspring to effectively stick to itself. Should you find your watch suddenly running wildly slow or fast, dont despair. A watchmaker can easily de-magnetize it in minutes, returning it to proper working order.
For reference, here are the Amperes/meter ratings of some common magnets.
35 A/m Earths magnetic field at its surface
4,000 A/m a typical refrigerator magnet
8,000 A/m a small iron magnet
5,500,000 A/m an MRI machine
6,600,000 A/m CERN Hadron Collider magnet