Reiteration in Theodolite
The method of
reiteration is another method of measuring horizontal angles. This method is
useful when a number of angles are to be measured at one point. In Fig. 6.7,
let O be the point where the instrument is set up and P, Q, R, and S be the
stations. Angle POQ, QOR, and ROS are to be measured. In the retiration method,
each angle is measured in succssion and finally the line of sight is brought
back to P, i.e., the line of sight is made to close the horizon. The instrument
is turned through 360 o . Obviously, the instrument should read, upon closing the
ho-rizon, the same reading set initially at P. The procedure is as follows.
1. Set up and level the theodolite at O. Keep the instrument in the
normal posi-tion, i.e., face left. Set the vernier at A to read zero using the
upper clamp and upper tangent screw. Check that the vernier at B reads 180 o .
2. Loosen the lower clamp and swing the instrument to bisect the
station mark P Tighten the swrew and using the lower tangent screw finaly bisect the signal
3. at at P. Check that the verniers at A and B read zero and 180 o ,
4. Release the upper plate with the upper clamp, swing the instrument
clockwise to bisect the signal at Q. Tighten the clamp and using the upper
tangent screw, bisect the mark at Q exactly.
5. Read the verniers at A and B and record both the readings.
6. Release the upper clamp screw, bisect the signal at R. Tighten the
clamp and bisect the mark at R exactly with the upper tangent screw. Read the
verniers at A and B and record the readings.
Continue the procedure with other stations.
-POQ = 68 o 32¢ 30?, -QOR =
61 o 41¢ 10?, -ROS = 102 o 54¢ 20?