Test: Levelling - 3 - Civil Engineering (CE) MCQ

If d is the distance to the visible horizon, it is given by,

‘C' being in metres,
∴ 

A change point is the point selected on the route before shifting the instrument. The change point is also called a turning point. The staff is kept on the turning point and a foresight is taken before shifting the instrument. The staff should not be moved when the instrument is being shifted. After the instrument has been shifted and set up at the new location, a back sight is taken on the staff still held at the change point.

Detailed Solution

Bench mark is a permanent reference point whose R.L is always known to us.

It is our first step to adjust the level for its temporary adjustment (centering, levelling) before start to take reading from a level.

Change point is a point which denotes shifting of level either due to inability to take reading or due to some obstruction

RL_B = RL_A + ∑BS - ∑FS
RL_B = 770.815 + 32.665 - 30.44
= 773.035
∴ Closing error = 773.035 - 772.940 = 0.10

Height = staff reading on floor + inverted staff reading 
= 1.40 + 3.67 = 5.07 m

The sensitivity of a bubble tube is given by