单项选择题
A.deviation minus variation B.variation plus compass course C.combined variation and deviation D.difference between true and magnetic heading
A.magnetism from the earth's magnetic field B.misalignment of the compass C.magnetism within the vessel D.a dirty compass housing
A.fore-and-aft and athwartships magnets B.dip needle and heeling magnet C.heeling magnet and Flinders bar D.Flinders bar and quadrantal spheres