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A Bench Mark (BM) with reduced level (RL) = 155.305 m has been established at the floor of a room. It is required to find out the Rl of the underside of the roof (R) of the room using spirit levelling. The back sight (BS) to the BM has been observed as 1.500 m whereas the fore sight (FS) to R has been observed as 0.575 m (staff held inverted). The RL (m) of R will be
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- 155.880
- 156.230
- 157.380
- 157. 860
- 155.880
Correct Option: C
RL of BM = 155.305 RL = reduced level
HI = RL of BM + BS BS = Back sight
= 155.305 + 1.500
= 156.805 m
FS to R = 0.575 (staff inverted)
∴ RL = 156.805 + 0.575 = 157.380 m at R
