http://www.ukclimbing.com/articles/page.php?id=5385
Maybe 40 years ago I heard of a guy whose compass got reverse magnetized in his glove compartment on the way to an orienteering meet, but it was close enough to 180 off that he did the meet using it backwards
Yes, it can happen. I have heard of the magnetic fields from NYC subway train motors doing the deed...
In any case, if the magnetization is changed, it will most likely be either too weak to be useful (ie the compass shows no preferred direction) or reversed (more likely). And as Roy noted, using a reversed compass backward is no problem if you know that it is reversed.
FWIW, AC (alternating) fields are used to demagnetize objects and DC (constant) fields tend to magnetize objects. The same applies to your compass.
The article neglects to mention that magnetic objects and electronic devices can alter the magnetic field that the compass is sensing without damaging the compass, causing inaccurate headings. Simply put some distance between the compass and the objects to eliminate the problem. (We often carry such objects/devices on our wrists, in our pockets, and in our packs.)
Magnetic rocks (eg Mt Hale summit, Katahdin Tableland) can similarly cause inaccurate compass readings.
Note: GPSes do not suffer from this problem.
Doug
