As stated earlier a bearing of a line is the angle made by the line with respect to a reference direction, the reference direction being known as meridian. The direction shown by a freely suspended and properly balanced magnetic needle is called magnetic meridian and the horizontal angle made by a line with this meridian is known as magnetic bearing.
The points of intersection of earth’s axis with surface of the earth are known as geographic north and south pole. The line passing through geographic north, south and the point on earth is called true meridian at that point and the angle made by a line passing through that point is called true bearing.
While traversing along lines A, B, C, D …, the bearing of lime AB is called fore bearing of AB
and the bearing of BA is called back bearing. Fore bearing and back bearing differ by 180°.