In reply to UKC/UKH News:
In addition to magnetic fasteners in clothing reversing the polarity of a compass stored close to the fastener there is also the magnetic field from a mobile phone to consider.
I think most, if not all, walkers carry a mobile now, either to use in an emergency or as check on their position. The magnetic field of a mobile is strong enough to cause deviation of a compass needle so even if a compass is kept well away from any magnetic closures there is a chance a bearing could be incorrect if the reading is taken close to a mobile stored in nearby pocket.