单项选择题
A.precession B.earth rate C.gyroscopic inertia D.gravity effect
A.remove deviation on the intercardinal headings B.remove deviation on the cardinal compass headings C.remove heeling error D.compensate for induced magnetism in vertical soft iron
A.reduce the variation as much as possible B.reduce the deviation as much as possible C.reduce the magnetic dip as much as possible D.allow the compass bowl to swing freely on its gimbals