Instrument required
1. Theodolite
2. Ranging rods
Diagram
Procedure
In this method the horizontal angle was measured twise or trise by allowing the verneir to remain clamp each time at the end of each measurement and thus the angle was added several times mechanically. However case should taken to add 3600 for every complete revolution. To the final reading. The average horizontal angle is then obtain by dividing the final reading by the number of repetition. The face then change and the whole process was repeated. Hence the average horizontal angle was obtained by taking the mean of the two values obtained from two faces.
