Definitions and Important Terms:
The instruments commonly used for angular measurements are the compass and theodolite. Before the study of instrument and procedures used for compass surveying, it is necessary to define some important terms commonly used in this context.
Bearing
The horizontal angle between the reference meridian and the survey line is termed as bearing of the survey line.
Magnetic Bearing
The magnetic needle of the compass always points towards the magnetic north-south (N-S) direction indicating earth's magnetic axis. Since this direction is same at all the places on the earth's surface, it is universally used as the reference direction. The angle made by survey line in a clockwise direction with reference to magnetic N-S line is termed as magnetic bearing of the line. The value of magnetic bearing ranges from 0o to 360o.