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TIL that it's highly nontrivial to figure out which direction true north is given magnetic north and your location on earth.
I had always assumed that you could treat the earth as a big magnet with the magnetic north pole in a slightly different place than true geographical north. but apparently the magnetic field of the earth is a really weird fucked up shape.
Meh? If 15° accuracy is good enough for you, that map of level curves shows you that most places on land will be fine, along with the parts of the ocean usually used for moving between land.