High quality analog compasses are designed for use within a certain area of the globe because the earths magnetic field not only varies horizontally, but also vertically, causing the needle to dip downward when the case is held level. The compass needle card is balanced with a small weight to counteract the downward dip, so the needle card does not drag or stick on the top or bottom of the capsule. If you take any compass to a significantly different part of the globe than where it was balanced, check the compass carefully before relying upon it. Our technical diving compasses are balanced either for the Northern Hemisphere or the Southern Hemisphere

Note that digital compasses, like the ones becoming popular in dive computers, do not have balance zones. Digital compasses are universal because they have a user 'calibration' feature, which is performed in the region where the diver plans to use the compass. A change in region simply requires a recalibration before use in a different location.