单项选择题
A.The Flinders bar
B.The heeling magnet
C.Quadrantal soft iron spheres
D.Bar magnets in the binnacle
单项选择题 The vertical angle between the horizontal and the magnetic line of force is the（）.
单项选择题 The total magnetic effects which cause deviation of a vessel’s compass can be broken down into a series of components which are referred to as（）.
单项选择题 The standard magnetic compass heading differs from the true heading by（）.