RL of BM = 211.800 m, staff reading at BM (BS) = 1.377 m, staff reading at station (FS) = 1.835 m. Calculate the RL of the station.
Correct Answer: A. 211.342 m
📚 Detailed Explanation: RL of Station = 211.342 m
Why A (211.342 m) is correct: The HI is calculated by adding the BS to the RL of the BM. Then the RL of the required station = HI − FS.
Given:
RL of BM = 211.800 m
BS reading at BM = 1.377 m
FS at required station = 1.835 m
RL of BM = 211.800 m
BS reading at BM = 1.377 m
FS at required station = 1.835 m
Step 1: Height of Instrument
HI = RL of BM + BS = 211.800 + 1.377 = 213.177 m
Step 2: RL of required station
RL = HI – FS = 213.177 – 1.835 = 211.342 m
Verification Using Rise and Fall
| Reading | Value (m) | Rise / Fall | RL (m) |
|---|---|---|---|
| BS at BM | 1.377 | — | 211.800 |
| FS at station | 1.835 | Fall = 1.835 − 1.377 = 0.458 | 211.800 − 0.458 = 211.342 ✓ |
Cross-check: Rise/fall method: FS > BS → Fall; Fall = 1.835 − 1.377 = 0.458 m. RL = 211.800 − 0.458 = 211.342 m. Agrees with HI method ✓.
- HI = 211.800 + 1.377 = 213.177 m.
- RL = 213.177 − 1.835 = 211.342 m.
- Cross-check via R&F: Fall = 1.835 − 1.377 = 0.458 m; RL = 211.800 − 0.458 = 211.342 m ✓.