1 - True North
2 - Heading, the direction the vessel is "pointing towards"
3 - Magnetic north, which differs from true north by the magnetic variation.
4 - Compass north, including a two-part error; the magnetic varation (6) and the ship's own magnetic field (5)
5 - Magnetic deviation, caused by vessel's magnetic field.
6 - Magnetic variation, caused by variations in earth's magnetic field.
7 - Compass heading or compass course, before correction for magnetic deviation or magnetic variation.
8 - Magnetic heading, the compass heading corrected for magnetic deviation but not magnetic variation; thus, the heading reliative to magnetic north.
9, 10 - Effects of crosswind and tidal current, causing the vessel's track to differ from its heading.
A, B - Vessel's track.

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