turning error

One of the errors inherent in a magnetic compass in which the compass lags behind the actual turn when turning through the north and leads when turning through the south in the Northern Hemisphere. The error is caused by the difference in the location of the pivot point and the center of gravity of the compass magnet system. The center of gravity of the magnet is placed below, but some radial distance from, the pivot. The acceleration forces in the turn—the centripetal and centrifugal forces—set up a couple in the vertical plane, which imparts a sideways tilt to the magnet system about the pivot. This is the main reason for the turning error. There are two other reasons for this error: first, the displacement of the center of gravity behind the pivot, and, second, the effect of liquid swirl. In the latter case, the liquid tends to rotate with the bowl and to drag the magnet system around with it. This increases the error in turns through the north in the Northern Hemisphere because the turning error itself causes the magnet to move in the opposite direction to the turn. This effect will be reduced in turns through the south. Also called northerly turning error. See northerly turning error.