READING MAGNETIC BEARING OF A LINE|Civil Easy Learning

READING MAGNETIC BEARING OF A LINE 

To find the bearing of a line AB as shown in fig .below 

reading-magnetic-bearing-of-line

i) Set up the instrument over A and level it accurately

ii) Set the vernier to the zero of the horizontal circle.

iii) Release the magnetic needle and loosen the lower clamp.

iv) Rotate the instrument till magnetic needle points to North. Now clamp the lower clamp with the help of lower tangent screw .Bring the needle exactly against the mark in order to bring it in magnetic meridian. At this stage the line of sight will also be in magnetic meridian.

iv) Now loose the upper clamp and point the telescope towards B .With the help of upper tangent screw ,bisect B accurately and read both the verniers .The mean of the two readings will be recorded as magnetic bearing of line.

v) Change the face of the instrument for accurate magnetic bearing of the line and repeat .the mean of the two values will give the correct bearing of the line AB.