Magnetic Bearing

It is termed as a survey line makes angle with respect to the magnetic meridian. It changes from location to location and based on MN. It is also defined as an angle between line and magnetic meridian. Angle is constantly measured in the clockwise direction. A freely balanced magnetic needle is utilized to illustrate the direction.

It is measure in relation to MN that is, using in the direction of the magnetic north pole. A compass points towards MN pole which is not true north.

Show the type of bearings as in Figure (1).

Show the connection among magnetic and true bearing as follows:

Positive sign is utilized when declination is towards west and negative sign utilized if the declination is towards east. Use positive sign when declination is towards east and use negative sign when declination is towards west.

Express the link between map and magnetic bearing as follows:

Following procedure explains the determination of bearing of a line AB as shown in Figure (2).

• Locate the apparatus over point A and level it precisely.
• Place vernier to zero of horizontal circle.
• Then release magnetic needle and loose lower clamp.
• Instrument is revolved till magnetic needle points to north. Lower tangent screw is utilized to fix lower clamp.
• To bring magnetic meridian, bring needle literally against the mark and line of sight at this state also is in magnetic meridian.
• After loosening upper clamp, spot the telescope in the direction of B.
• Then intersect B exactly and read both venires with the aid of upper tangent screw.
• Magnetic bearing of a line is recorded from mean of two readings.
• Finally, change the instrument face for exact magnetic bearing of line and do again the procedure.
• Correct bearing of line AB is attained by averaging of above two values.