MEASUREMENT OF HORIZONTAL ANGLES BY
To measure the horizontal angle between the ‘OA’ and ‘
O – Instrument Station
A – Ranging Rods No.1
B – Ranging Rod No.2
(iii) Ranging Rods
The method of repetition is used to measure the horizontal angle to a finer degree of accuracy than that obtainable with the least count of the vernier. By this method an angle is measured two (or) more time by allowed the vernier to remain clamped each time at the end of each measurement of the previous station. Thus an angle reading is mechanically repitions. The average horizontal angle is then obtained by dividing the final reading by number of repitions.
To measure the angle of horizontal AoB, the following Procedure:
· Set the instrument at station ‘O’ and level it with the help of alidade bubble and foot screw. Set zero reading (or) vernier A note the reading at vernier B.
· Loose the lower clamp and direct the telescope towards the point ‘A’ accurately by lower tangential screw.
· Then unclamp the upper clamp and turn the instrument clockwise about inner axis towards ‘B’ accurately with the upper tangential axis.
· Unclamped the lower clamp and turn the telescope N sight A. Again bisect ‘A’ accurately by using the lower tangential screw. It should be noted that the vernier reading will not be changed in this operation. Since the upper plate is clamped to the lower.
· Unclamp the upper clamp; turn the telescope clockwise and Sight ‘B’ accurately by upper tangent screw.
· Repeat the process until the angle i.e. for repeated no. of times say three times. The average angle with face left will be equal to the final reading divided by number of repetition (3)
The horizontal angle between the two points is found out by the method of repetitions using theodolite and found as -------------------