Compass card

Magnetic marine compasses have magnets fastened to a circular card which has the directions printed on it. Traditionally, compasses were marked in points at every 11 1/4 degrees. The whole card rotates, and a mark on the compass housing (called a lubber line) indicates direction. Until the mid 19th century, compasses were "dry card;" that is, the compass card rotated in air on a pivot pin. Edward S. Ritchie developed the first liquid magnetic compass (or wet card compass) in 1862, which solved problems of instability in dry card compasses. Wet card compasses have the card suspended in a liquid, usually a light oil, which has a float in the center to take most of the weight of the card off the pivot. The oil damps or smooths the card motion in a rough sea. Modern compasses are marked in degrees from zero at the north around to 359.