Mike, You don't have to do anything to your compass if you go south of the equator. The magnet inside your compass aligns itself with the horizontal component of the earth's magnetic field. At the equator, that magnetic field is parallel to the earth's surface. It becomes vertical at the North and South poles, which is why magnetic compasses don't work in those regions. (the horizontal component becomes so small that the compass becomes useless.) All you have to worry about is the difference between magnetic and true north in your sailing area, when laying out a course, which you will find on your nautical charts. Connie