The main advantage of the rise and fall method of booking levels over the height of instrument method is that it:
Correct Answer: B. Provides a check on intermediate sights
📚 Detailed Explanation: Rise and Fall Method Checks Intermediate Sights
Why B (Checks accuracy of intermediate sights) is correct: The main advantage of the Rise and Fall (R&F) method over the Height of Instrument (HI) method is that R&F arithmetically checks every staff reading, including intermediate sights (IS). The HI method does not check IS readings arithmetically.
Comparison: Rise and Fall vs. HI Method
| Feature | Rise and Fall Method | HI (Collimation) Method |
|---|---|---|
| ΣBS − ΣFS check | Yes ✓ | Yes ✓ |
| Checks Intermediate Sights (IS) | YES — IS errors appear in rise/fall column and fail the ΣRise − ΣFall check | NO — IS errors do not affect any check; can go undetected |
| Field booking speed | Slower (more columns) | Faster (fewer columns) |
| Where preferred | Cross-sections, profiles with many IS readings where accuracy matters | Rapid levelling where few IS readings are needed |
Rise and Fall: 3 independent checks
(1) ΣBS – ΣFS = Last RL – First RL
(2) ΣRise – ΣFall = Last RL – First RL
(3) ΣBS – ΣFS = ΣRise – ΣFall
(1) ΣBS – ΣFS = Last RL – First RL
(2) ΣRise – ΣFall = Last RL – First RL
(3) ΣBS – ΣFS = ΣRise – ΣFall
If an IS reading is wrong, checks (2) and (3) will FAIL, alerting the surveyor.
HI method: only 1 check
ΣBS – ΣFS = Last RL – First RL
IS errors do NOT appear in this check.
- Rise and Fall's key advantage: checks accuracy of intermediate sights (IS).
- HI method cannot detect IS errors through its arithmetic check.
- When IS accuracy matters (many IS readings), R&F is the preferred method.