Compass

An instrument that indicates direction relative to a defined north reference.

A magnetic compass aligns with the local horizontal component of the Earth’s magnetic field and indicates magnetic or compass direction. Gyrocompasses and electronic heading systems use different principles and may indicate true or calculated heading when correctly configured.

A magnetic compass is affected by variation and by deviation from magnetism aboard the vessel; it also has dynamic and installation errors. It remains useful independently of satellite positioning, but must be read, illuminated, adjusted and compared with other information appropriately.