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» » » MEASUREMENT OF HORIZONTAL ANGLE BY REPETITION METHOD
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Aim: To measure the horizontal angles between the given stations about the instrument station as the vertex by the method of reiteration.

Instruments and Accessories Required:
            Theodolite, Pegs, Arrows,Ranging Rod,etc.

Procedure:
  1. The theodolite is mounted on the tripod stand.
  2. The theodolite is centered over an arbitrarily selected station P from where the given stations can be sighted without any obstruction and the instrument is levelled using the foot screws and the plate bubble is brought to the centre of the run.
  3. The theodolite is set on the face right mode on the vernier A  and the horizontal circle is initially set at 0°00’00” and the station A is sighted .
  4. The upper clamp screw is unclamped and the theodolite is swung to the right and the station B is sighted and the central vertical cross hair is made to bisect this station and the horizontal angles on both the vernier A and B are observed.
  5. The measurement of horizontal angle between the stations A and B is repeated for the desired number of repetitions and the cumulative horizontal angle observed in the last repetition is recorded.
  6. The theodolite is then set on the face left mode and the vernier A on the horizontal circle is initially set at 180°00’00” and the station B is sighted.
  7. The upper clamp screw is unclamped and the theodolite is swung to the left and the station A is sighted and the central vertical cross hair is made to bisect this station and the horizontal angles on both the vernier A and B are observed.
  8. The measurement of horizontal angle between the station A and B is repeated for the same number of repetitions as earlier and the cumulative horizontal angle observed in the last repetition is recorded.
  9. The observations are recorded in the field book.
  10. The mean values of the horizontal angles on vernier A and B are computed for every sighting.
  11. The actual horizontal angle between the given stations is determined by dividing the cumulative horizontal angle by number of repetitions.
  12. The average of the two actual horizontal angles observed on each for the two initial settings of vernier A is determined as the result.






Tabulation

Inst at
Sighted to
Horizontal Circle Reading
Included Angle
Average Included Angle
Remarks
Vernier A
Vernier A
Mean
°
°
°
°

FACE RIGHT
















P
A










































































FACE LEFT
















P
B











































































Result: The horizontal angles between the given stations about the instrument station as the vertex are determined by the method of repetition.
            Angle APB =

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