MEASUREMENT OF HORIZONTAL ANGLES |Ordinary Method |Civil Easy Learning

MEASUREMENT OF HORIZONTAL ANGLES: 

1) Ordinary Method. To measure horizontal angle AOB:-

Ordinary Method

  

i) Set up the theodolite at station point O and level it accurately.

ii) Set the vernier A to the zero or 360degrees Of the horizontal circle. Tighten the upper clamp.

iii) Loosen the lower clamp. Turn the instrument and direct the telescope towards A to bisect it accurately with the use of tangent screw. After bisecting accurately check the reading which must still read zero. Read the vernier B and record both the readings.

v) Loosen the upper clamp and turn the telescope clockwise until line of sight bisects point B on the right hand side. Then tighten the upper clamp and bisect it accurately by turning itstangent screw.

v) Read both verniers. The reading of the vernier a which was initially set at zero gives the value of the angle AOB directly and that of the other vernier B by deducting 180 degrees. The mean of the two vernier readings gives the value of the required angle AOB.

vi) Change the face of the instrument and repeat the whole process. The mean of the two vernier readings gives the second value of the angle AOB which should be approximately or exactly equal to the previous value.

vii) The mean of the two values of the angle AOB ,one with face left and the other with face right ,gives the required angle free from all instrumental errors.