Just before World War I the gyroscopic compass appeared on the scene. The gyro compass is an electro mechanical device which basically functions like a gyroscopic top. When spinning and lined up with the meridian it holds that position regardless how the the ship moves around. It is not affected by deviation and variation and there is only one error, called gyro error. It is determined periodically by use of shoreside ranges or bearings of celestial bodies. These bearings are called Azimuths or, in special circumstances, Amplitudes. In either case one must compare the bearing as observed against the bearing as calculated. The difference is the gyro error. It is named East or West and has an amount, usually less than a degree. Thus the gyro compass comes closest to indicating Geographic North.
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