单项选择题
A.It compensates for the error caused by the vertical component of the Earth's magnetic field
B.It compensates for error caused by the heeling of a vessel
C.It compensates for quadrantal deviation
D.It is only needed in equatorial waters
单项选择题 Which magnetic compass corrector（s）CANNOT be set on a heading of magnetic east or magnetic west（）.
单项选择题 Which magnetic compass corrector（s）can be set while the vessel is on a heading of magnetic north or magnetic south（）.
单项选择题 Which compensates for errors introduced when the vessel heels over（）.