Differential levelling (also called spirit levelling) is primarily used to:
Correct Answer: D. Difference of elevation between two points
📚 Detailed Explanation: Differential Levelling Is Used to Find Difference in Elevation
Why D (Find difference of elevation between two points) is correct: Differential levelling (also called fly levelling or spirit levelling) is the fundamental technique used to determine the difference in height between two points that may be separated by considerable distance, with the instrument moved progressively along the route.
Types of Levelling and Their Applications
| Type of Levelling | Primary Application |
|---|---|
| Differential levelling | Determine the difference in elevation between two widely separated points (which cannot be seen from a single instrument position) |
| Profile (longitudinal section) levelling | Determine elevations of points along a line (road, pipeline, canal alignment) |
| Cross-section levelling | Determine ground levels perpendicular to a centre line (for earthwork quantity calculations) |
| Reciprocal levelling | Determine precise elevation difference across a wide obstacle (river, gorge) that cannot be bridged by a single setup |
| Trigonometric levelling | Determine elevation using vertical angles (indirect levelling; used in hilly terrain) |
- Differential levelling = find the difference in elevation between two points.
- Multiple instrument setups between the two points are connected by change points (CPs).
- The algebraic sum of all rises and falls equals the total height difference.