but if magnetic attraction was precisely the same everywhere on earth then, (I THINK), what you're thinking would be correct... but magnetic attraction is not the same everywhere due to MANY factors... some geographical... some more immediate surroundings - for example in a plane. Each plane's compass is calbrated for the deviation caused by the compass itself in the plane and the plane itself. So if the magnetic declination is "X" for your locale it's further adjusted for the effect the plane has on the compass.

Locale... weather, iron in the earth, many things work like the "plane" in my example above. So these have to be factored in to get a true reading of both magnetic north AND true north. Magnetic north fluctuates, but slowly, so it's basically always in the same place... but the 'deviation' caused by soil, weather, etc... is different everywhere on earth. - JamesJM



Edited 1 time(s). Last edit at 07/07/2020 02:34PM by JamesJM.