单项选择题
A.worn gears in the compass housing B.magnetism from the earth's magnetic field C.magnetism within the vessel D.lack of oil in the compass bearings
A.deviation B.variation C.compass error D.northerly error
A.the compass heading is in line with the lubber's line B.there is no lost motion in the gimbal rings C.no change of heading by compass is observed if you raise and lower the heeling magnet D.the gimbal rings do not strike the compass frame when they are tilted