The levelling method in which both staff readings and the distance between points are required is called:
Correct Answer: B. profile levelling
📚 Detailed Explanation: Profile Levelling Requires Both Staff Readings and Distances
Why B (profile levelling) is correct: Profile levelling (also called longitudinal sectioning) involves recording the ground elevation at regular measured horizontal intervals along a route. Because both the height (staff reading) and the chainage (horizontal distance along the baseline) are needed to plot the longitudinal section, it is the only levelling method that requires both pieces of information simultaneously.
Comparison of Levelling Methods: Data Required
| Method | Staff Readings Needed? | Distances Needed? | Purpose |
|---|---|---|---|
| Fly Levelling | ✓ YES (BS & FS only) | ✗ Not essential | Quick elevation check; establish/verify BMs |
| Profile Levelling | ✓ YES (BS, IS, FS) | ✓ YES (chainage at each station) | Longitudinal section; route design for roads, canals, pipelines |
| Differential Levelling | ✓ YES | ✗ Not required for RL calculation | Find RL difference between distant points |
| Reciprocal Levelling | ✓ YES | ✗ Not essential | Level across wide obstacles |
| Block Levelling | ✓ YES (at grid nodes) | ✓ YES (grid coordinates) | Contouring an area; both coordinates and heights |
- Profile levelling = the only levelling method that always requires both staff readings (heights) and horizontal distances (chainages).
- Output: a longitudinal section (profile) drawn to scale with H and V axes.
- Used for: road alignment, canal design, railway earthwork computation.