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If the staff is not held vertical at a level¬ling station, the reduced level calculated from the observation would be
Answer & Solution
Correct Answer:
Option
C
In levelling, it is essential that the staff is held vertically at the observation point.
If the staff is tilted (not vertical), the horizontal distance between the instrument and the staff increases slightly.
This results in the levelling instrument recording a reading higher than it would if the staff were vertical.
Since the reading is higher, the calculated Reduced Level (R.L.) becomes lower than the actual or true R.L.
Therefore, a non-vertical staff leads to a reduced level that is less than the true reduced level.
Hence, the correct answer is Option C: less than true R.L.
If the staff is tilted (not vertical), the horizontal distance between the instrument and the staff increases slightly.
This results in the levelling instrument recording a reading higher than it would if the staff were vertical.
Since the reading is higher, the calculated Reduced Level (R.L.) becomes lower than the actual or true R.L.
Therefore, a non-vertical staff leads to a reduced level that is less than the true reduced level.
Hence, the correct answer is Option C: less than true R.L.
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LoginLet RL of observation point =100m
Case-1 ( when staff is tilted towards the observation point)
In this case the staff reading will be more than if the staff was held exactly vertical.
Hence the RL of the staff point will more.
Case-2 (when staff is tilted outward of the observation point)
In this case staff reading will be less and hence the RL of staff point will be less than if it was held exactly vertical.
So both options b and c are correct.
Then , if a staff stands without any error
ans that it should be straight ... F. S is 2 m ( assume).
Then the staff R. L = 100-2 = 98m...
Now, if the staff not held vertically means inclined. Then it must be reading more than 2 m ( assume first).
Because of, we know that straight lines is shortest distance between two point as in the first case...
This staff reading is 3 m ( suppose)..
The R. L. OF the staff is 100-3 = 97 m....
So according to this theory answer is option 3