Magnetic compass

According to historical details from Wikipedia's article "History of the compass", the device evolved over two millennia from early Chinese lodestones to liquid-filled marine instruments introduced in the early 20th century. On a modern yacht, the magnetic compass remains the primary non-electronic instrument for directional orientation.

It is essential to distinguish the magnetic compass from a gyrocompass or a standard hiking compass. Unlike electronic sensors, a magnetic compass responds directly to the Earth's magnetic field, indicating magnetic north rather than true geographic north. The angular difference between true north and magnetic north is termed magnetic variation (Var), measured in degrees East or West. Additionally, magnetic interference from onboard equipment causes compass deviation (Dev). To obtain the true heading (TH) from the compass heading (CH), navigators apply the formula: TH = CH + (±Var) + (±Dev).

A standard marine compass features a card graduated from 0° to 360°, submerged in a damping liquid within a compass bowl, and mounted on gimbals to withstand vessel heel and pitch. Knowing how to use a marine compass is critical when preparing passage plans alongside accurate weather forecasts. Even in an era dominated by GPS, the magnetic compass provides an unshakeable backup that requires zero electrical power.