Map, Compass & GPS

Map, Compass & GPS
Wild flowers along Fall Creek on the way to the Green Lakes - Oregon

Monday, November 24, 2014

Compass Deviation

Compass deviation is not declination.  As a Royal Australian Naval Officer told me years ago, "it is man's earthly sins" that give us deviation.  So just what is it?

Deviation is the deflection of a compass' magnetic needle due to natural or man made interference.

Natural deviation is cause by iron or nickel deposits near the surface of the earth.  Such deflection may also be called "natural attraction."  Further, on a small scale, natural objects such as belt buckles, and rifle barrels may also cause error too.

Man made deviation is caused by electrical circuitry (e.g., florescent lighting), the electronics of a car, significant power line systems and the body of a vehicle.  Notice that being inside a structure will also impact and deflect the magnetic compass needle too.

Over the 15 years of teaching compass navigation I have had two or three people tell me that they had wrapped their compass' lanyard around GPS and compass  and left the intertwined units on the dashboard of their truck.  They claimed that this effected the polarity of the magnetic needle.  Interesting to consider.

So, how is the deflection removed or canceled?  Move.  Move away from the power lines, move the rifle barrel and other ferrous objects. (Move at least a hundred feet from power lines.)

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