It is important for a compass needle to rotate freely. But the amount of magnetism is not the same all over the globe. For this reason most of the compasses we sell have needles that are balanced for the northern hemisphere -- which work great in the USA and most of Europe. But when one of those compasses gets near the equator, or goes below the equator, the needle will be off balance, and not rotate freely.
The compasses on this page have been designed with a global needle that can handle greater tilts, and allow the compass needle to rotate freely inside the capsule, all over the world -- even in the southern hemisphere.