Associate
You can NEVER go wrong with a no-date Sub.
Picked up a non date submariner today on a little visit to Osaka, Japan before heading to Tokyo
In what weekly or monthly situation even do you encounter where there is a magnetic field? Can't say the 2 or so years of owning mine that this has been a concern at all whether it was in a flight or the Arctic circle or surrounded by a room full of computer equipment.
It really is a case of "my watch has this but in the real world it doesn't mean much".
As someone said, MRI. Also magnetic testing. My boss magnetised his Breitling a little while back. A smallish neodymium magnet is enough to set a watch running wonky.