Compass Card

The compass card is the graduated disc, marked 0 to 360 degrees (and traditionally in 32 points), that shows the heading against the lubber line. In a magnetic compass the card is attached to the magnets and floats in liquid, so the card stays aligned with magnetic north while the bowl and lubber line turn with the ship. The reading is a compass heading that must be corrected for deviation (the ship’s own magnetism) and variation (local geomagnetic offset) to give true.