# INVERTED COMPASS

A marine magnetic compass designed and installed for observation from below the compass card. Frequently used as a telltale compass. Also called HANGING COMPASS, OVERHEAD COMPASS.

## Related Terms

### ARMATURE DEMAGNETIZATION

The reduction in the effective magnetic lines of force, produced by the armature current.

### AIR GAP

The space between magnetic poles, or between the rotating and stationary assemblies in a motor or generator.

### GYRO ERROR

The error in the reading of the gyrocompass, expressed in degrees east or west to indicate the direction in which the axis of the compass is offset from true north.

### HALVING

The process of adjusting magnetic compass correctors so as to remove half of the deviation on the opposite cardinal or adjacent intercardinal headings to those on which adjustment was originally made when all deviation was removed. This is done to equalize the error on opposite headings.

### HALVING

The process of adjusting magnetic compass correctors so as to remove half of the deviation on the opposite cardinal or adjacent intercardinal headings to those on which adjustment was originally made when all deviation was removed. This is done to equalize the error on opposite headings.

### HEELING MAGNET

A permanent magnet placed vertically in a tube under the center of a marine magnetic compass, to correct for heeling error.

### HORIZON PRISM

A prism which can be inserted in the optical path of an instrument, such as a bubble sextant, to permit observation of the visible horizon.

### GRID MAGNETIC ANGLE

Angular difference in direction between grid north and magnetic north. It is measured east or west from grid north. Grid magnetic angle is sometimes called GRID VARIATION or GRIVATION.

### GYROCOMPASS

A compass having one or more gyroscopes as the directive element, and which is northseeking. Its operation depends upon four natural phenomena, namely gyroscopic inertia, gyroscopic precession, the earth's rotation, and gravity. When such a compass controls remote indicators, called GYRO REPEATERS, it is called a master gyrocompass.