Theory
The term deflection angle is used to mean the angle made by survey line to the extension of the preciding line.
Instrument required
1. Theodolite
2. Ranging rods
Diagram
Procedure
1. The instrument was setup and level accurately at station ‘O’
2. Both the plates wear clamped at ‘O’ level and back sight was taken on station point.
3. The upper plot was in clamped and the fore sight of the station ‘O’ was taken. The reading on both the verniers were recorded.
4. The lower clamp was unclamped and the instrument was shifted to station ‘P’ again. There was no change in the reading as recorded in step three above.
5. The process was repeated and the instruments was again sighted to ‘Q’. The readings on both verneirs are recorded.
6. As the deflection angle was doubled because of taking both face reading. The average value of deflection angle was obtained by dividing the final reading by two.
