# SEMICIRCULAR DEVIATION

Deviation which changes sign (E or W) approximately each 180° change of heading.

## Related Terms

### 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half of the deviation on the opposite cardinal or adjacent intercardinal headings to those on which adjustment was originally made when all deviation was removed.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 ERROR

The change in the deviation of a magnetic compass when a craft heels, due to the change i

### LANDING COMPASS

A compass taken ashore so as to be unaffected by deviation. If reciprocal bearings of the landing compass and the magnetic compass on board are observed, the deviation of the latter can be determined.

### DEVIATION

A vessel distance from specified voyage course

### MAGNETIC MERIDIAN

A line of horizontal magnetic force of the earth. A compass needle without deviation lies in the magnetic meridian.

### MAGNETIC RANGE

A range oriented in a given magnetic direction and used to assist in the determination of the deviation of a magnetic compass.

### COEFFICIENT

1. A number indicating the amount of some change under certain specified conditions, often expressed as a ratio. For example, the coefficient of linear expansion of a substance is the ratio of its change in length to the original length for a unit change of temperature, from a standard. 2. A constant in an algebraic equation. 3. One of several parts which combine to make a whole, as the maximum deviation produced by each of several causes.

### COEFFICIENT E

A component of magnetic compass deviation varying with the cosine function of twice th

### COEFFICIENT A

A component of magnetic compass deviation of constant value with compass heading resulting from mistakes in calculations, compass and pelorus misalignment, and unsymmetrical arrangements of horizontal soft iron.