How Do Compasses Work in the Southern Hemisphere?
Faculty resources from the Biology Department at Williams College explain that there are northern- and southern-hemisphere compasses that only work in their respective hemispheres. The reason for this is that a compass needle aligns itself to the Earth’s magnetic field, and the lines of this field point to the north and south poles.
A compass needle has two ends that are painted different colors, with red indicating north. When a compass is in the northern hemisphere, the north end of the needle is pulled down towards the Earth, so the south end must be counterweighted to balance it. If a northern-hemisphere compass is used south of the equator, the south end of the needle is pulled down instead. Since the south end is already weighted, this pull causes it to drag on the bottom of the compass, resulting in less than accurate readings. A compass designed for the southern hemisphere is weighted differently to avoid this problem.
According to Geokov, some manufacturers produce high-quality global compasses that work in any region, but most standard compasses are intended for use within a specific zone. There are some places where any compass becomes entirely unusable. A close proximity to the north or south pole results in inaccurate readings because of a sharp increase in magnetic inclination.