I just picked up THE 2 OZ. BACKPACKER by Robert S. Wood by ten speed press www.tenspeed.com this is a wonderfull book with some interesting insights. The author points out that 1 degree of error in a mile amounts to 92' My Brunton surveying compass is 1 degree accurate. Most dedicated hiking or orienteering compasses are accurate to 2 degrees and the smaller units 5. My Brunton button unit is @ 10. I've used the button compass in the city with good results. There are many tools in navigation; charts,compasses, known landmarks and that intangible inner sense.The button has been most usefull in calibrating my "inner compass" with the other tools.