The reduced level of a floor is 99.995 m, the staff reading on the floor is 1.505 m. If the inverted staff reading against the roof is 1.795 m, the floor level below the slab, is

ANS:B - 3.300 m

HI = RL + Staff reading on floor.
= 99.995 + 1.505 = 101.5m.

Here the staff was inverted against the roof and the staff reading is 1.795m.
So, HI + inverted staff reading.
= 101.5 + 1.795 = 103.295m.
So floor level = 103.295 - 99.995 = 3.3m. H.I of Instrument = 99.995+1.505 = 101.5 m.
As the second staff reading is negative this,
= 99.995-1.795= 98.2m.
= 101.5 - 98.2 = 3.3m answer. If the benchmark of a station 'A' is 100, Back sight is 1.4m, foresight is 1.5m then what will be the level of the line of sight? H.I = R.L+B.S.
= 99.995+1.505.
= 101.5.

The Floor Level Below The Slab = H.I+Inverted Staff Reading.
= 101.5+1.795.
= 3.30m. We can know, the distance between the floor and slab is always near around 3 m so answer we can predict options which are near about 3 m and second the technical specifications in the questions staff is held inverted so the b.s- f.s= 1.505-(-1.795 ) (- because staff is inverted) and answer is 3.3 m.