Storing a compass in or near metal objects will not effect permanent deviation in the magnetic heading. USING a compass on, or near a metal object while taking a bearing will cause a incorrect reading. The value in owning multiple units is A. a ready reference for accuracy and B.redundancy in case of loss. I keep my old Silva ranger unit stored in my rucksack. My button compass lives in my PSK. When I go anywhere with the ruck several items immediately go onto my person; compass into chest pocket,whistle onto neck lanyard and knife to sheath.