Direction at sea once depended on a single instrument. A compass is a device that indicates direction relative to the Earth’s magnetic field or, in modern form, relative to true north via gyroscopic or electronic means.

Magnetic compasses still serve as the required backup on most ships. Gyrocompasses provide true north and feed repeaters around the vessel. Fluxgate and satellite-derived heading systems add further options. All compasses need checking and, for magnetic types, correction for deviation.

Navigators compare compass headings with visual and radar bearings to detect errors. A failed gyro with no magnetic backup can leave a ship without reliable heading reference. Regular compass swings and error logs remain standard practice.

• Instrument indicating direction relative to north
• Includes magnetic, gyro, and electronic types
• Requires calibration and error monitoring
• Essential backup even with satellite navigation