单项选择题
Deviation in a compass is caused by the（）.
A.vessel's geographic position B.vessel's heading C.earth's magnetic field D.influence of the magnetic materials of the vessel
单项选择题 Compass error is equal to the（）.
单项选择题 Compass deviation is caused by（）.
单项选择题 Before a magnetic compass is adjusted certain correctors must be checked to ensure that they are free of permanent magnetism. These correctors are the（）.
