In which of the following types of level is the telescope rigidly fixed to the levelling head (and can only rotate about the vertical axis)?
Correct Answer: A. Dumpy level
📚 Detailed Explanation: Dumpy Level Has Telescope Rigidly Fixed to the Levelling Head
Why A (The telescope is rigidly fixed to the level, which can only rotate about the vertical axis) is correct: The defining characteristic of a dumpy level is that the telescope is permanently and rigidly attached to the levelling head. It cannot be tilted or rotated about the horizontal axis; it can only rotate in plan (about the vertical axis).
Types of Levels and Their Distinguishing Features
| Instrument | Key Feature | How Levelled |
|---|---|---|
| Dumpy level | Telescope RIGIDLY fixed to levelling head; cannot tilt | Three-foot screws + long bubble tube |
| Tilting level | Telescope can be tilted (tilted) about a horizontal axis; separate tilting screw | Rough-level with ball-and-socket + precise-level with tilting screw + coincidence bubble |
| Automatic (self-levelling) level | Uses a compensator (pendulum or prism) to automatically keep line of sight horizontal within a working range | Rough-level with circular bubble; compensator does fine levelling automatically |
| Wye (Y) level | Telescope held in Y-shaped clips; can be lifted and reversed in clips; allows permanent adjustment testing | Four-screw plate; older type; largely replaced by dumpy |
Memory Aid for Dumpy Level: “Dumpy” refers to the short, stubby appearance of the instrument — but technically it refers to the rigid (fixed) connection between the telescope and the levelling head. It cannot be “tilted” separately.
- Dumpy level: telescope rigidly fixed to levelling head; only rotates about vertical axis.
- Cannot be tilted independently (unlike tilting level or auto level).
- Most basic and robust level type; very stable once properly levelled.