Join Date: Aug 2006
Location: Arlington, VA
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Compasses made for use in the northern hemisphere sometimes have a counterweight on the south end, since as you near the north pole there is a magnetic attraction downwards which, left uncorrected, in some compasses could cause the needle to scrape the housing.
Those made for use in the southern hemisphere have the counterweight on the north end.
This is only a problem with small compasses which have very little clearance for the needle to move up and down. Not usually a problem with marine compasses, which generally can be used in both hemispheres without problems.
I'm an affectionado of hand-bearing compasses, but have for some years used a better solution: a good pair of binoculars with a built-in compass. I use Fujinon's Polaris model, and with these it is very easy to take accurate magnetic bearings.