What is Compass Adjustment?

A Compass Adjustment is the method of analyzing and compensating for deviating forces of a vessel’s magnetic compass.

A magnetic compass should always align steadily to the earth’s magnetic field, pointing to magnetic north. However, steel, electronic instruments or equipment, and even the type of cargo carried, can cause the compass needle to point away, or deviate, from magnetic north. Compass adjustment is necessary to compensate these deviating forces with correctors. The deviations on principle headings, typically the cardinal (N, E, S & W) headings and intercardinal (NE, SE, SW & NW) headings are identified, and then correctors are employed to either completely remove or reduce the deviation. Correctors may be permanent magnets or soft iron, which are placed adjacent to the compass. This creates equal, but opposing magnetic fields, thus nullifying the deviating fields around the compass, enabling it to align correctly. Now, the earth’s magnetic field can pass through the compass without being deflected out of its normal path. For various factors such as design, location and the vessel’s unique magnetic properties, all the deviation may not be removed. The residual deviation is recorded on a deviation card as a table or a curve of deviation against the compass headings.