# In Levelling Operation

By BYJU'S Exam Prep

Updated on: September 25th, 2023

In levelling operation-

1. The first sight on any change point is a back sight
2. The second sight on any change point is a fore sight
3. The line commences with a fore sight and closes with a back sight
4. The line commences with a back sight and closes with a foresight.

1. 1 and 2 are correct
2. 1 and 3 are correct
3. 2 and 3 are correct
4. 1 and 4 are correct

Answer: D. 1 and 4 are correct

## In levelling operation, the first sight on any change point is a back sight and the line commences with a back sight and closes with a foresight.

Solution

Back Sight: Back sight is the first sight taken by the levelling instrument at the benchmark (benchmark is point of known elevation).

Fore sight: Fore sight is the last sight taken by the levelling instrument at any point which RL needs to calculate.

Intermediate Sight: It is the reading at any station taken between back sight reading and fore sight reading.

NOTE: In case of change point, the first sight taken by the instrument is the back sight which is generally taken as the last station of previous instrument position which is used to establish the reduced level of height of instrument after change point.

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