Which of the following is an INCORRECT feature of the auto level instrument used for levelling?
Correct Answer: B. Readings on the staff are taken automatically
📚 Detailed Explanation: INCORRECT Feature — Auto Level Does NOT Read Staff Automatically
This question asks for the INCORRECT feature. The answer is B: “Readings on the staff are taken automatically.” This is false — the auto level’s compensator only stabilises the line of sight; the surveyor still reads the staff manually through the telescope.
Evaluation of Each Option
| Option | Statement | True or False? | Explanation |
|---|---|---|---|
| A | Instrument levelled roughly with foot screws | ✓ TRUE | Auto levels have a circular bubble and three foot screws; the instrument is roughly levelled by the surveyor using these, then the compensator takes over for fine levelling of the line of sight |
| B | Readings on the staff are taken automatically | ✗ FALSE (INCORRECT feature) | Only the line of sight is automatically levelled by the pendulum/prism compensator. The surveyor must still look through the eyepiece and manually read the staff graduations. No auto level has an automatic staff-reading function. |
| C | Readings on the staff are taken manually | ✓ TRUE | Correct — this is the actual behaviour; surveyor reads the staff through the telescope |
| D | Works on compensator mechanism | ✓ TRUE | The core feature of auto levels is the internal compensator (pendulum or prism type) that automatically keeps the line of sight horizontal within a small range (±10′ to ±15′ of tilt) |
How the Auto Level Compensator Works
| Step | Action |
|---|---|
| 1 | Surveyor roughly levels instrument using circular bubble and foot screws |
| 2 | Internal compensator (pendulum mirror or prism) hangs by thin wires |
| 3 | Gravity keeps the compensator element horizontal regardless of minor instrument tilt |
| 4 | This automatically directs the line of sight to be horizontal |
| 5 | Surveyor reads staff graduation through the telescope manually |
- INCORRECT feature: “Readings taken automatically” — the compensator levels the line of sight, not the staff reading.
- Auto level does NOT automatically read staff values; the surveyor reads manually.
- The compensator works within a tilt range (typically ±10′–15′); beyond this, the bubble goes outside the ring and the instrument must be re-levelled.