---
title: "Short note: sources of error in levelling"
subject: "Surveying I"
chapter: 5
key: "semester_3/surveying_i:short-note-sources-of-error-leveling"
source: https://www.bctengineer.com/q/semester_3/surveying_i/short-note-sources-of-error-leveling
site: BCT Engineering
---

# Short note: sources of error in levelling

Surveying I · Chapter 5: Leveling

- Asked in: 2074 Asoj, 4 marks
- Video: [Errors in Leveling - Levelling and Its Application - Surveying 1](https://www.youtube.com/watch?v=b3h_czrxzVA) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/short-note-sources-of-error-leveling
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-5

## Question

Write a short note on sources of error in levelling.

## Short answer

Errors are instrumental (collimation, sluggish bubble, staff graduation, parallax), natural (curvature, refraction, temperature, wind, settlement), and personal (bubble not centred, staff not vertical, wrong reading/booking, change point moved, calculation mistakes). Balance sights, keep distances short, and centre bubble to minimize.

## Answer

Errors in levelling are classified as instrumental, natural, and personal errors.

#### 1. Instrumental errors

- **Collimation error:** the line of collimation is not parallel to the axis of the bubble tube; removed by balancing sights or by permanent adjustment (two-peg test).
- Bubble tube not adjusted, sluggish bubble.
- Staff not correctly graduated; wear and tear of the staff foot, bent staff, or loose joint (telescopic staff).
- Parallax due to improper focusing.

#### 2. Natural errors

- **Curvature of the earth:** makes the staff readings too high, $C_c = 0.0785\,d^2$ (d in km, correction in m).
- **Refraction:** bends the line of sight downward, so readings are too low, $C_r = \dfrac{1}{7}C_c$.
- Temperature changes causing unequal expansion of the instrument and heat shimmer; wind causing vibration; settlement of the tripod or of the staff in soft ground.

#### 3. Personal errors

- Bubble not centred at the time of reading.
- Staff not held vertical; wrong reading (e.g. reading 1.234 as 1.324) or inverted figures; wrong booking.
- Staff not held on the same point at the change point.
- Mistakes in calculation (wrong addition or subtraction, wrong sign).
- Wrong focusing or sighting in a hurry.

**Minimising the errors:** balance the sights, test and adjust the level, keep the sights short (about 60–100 m), hold the staff vertical, avoid the lowest part of the staff, and apply the arithmetic checks.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Errors in levelling are classified as:
   A. Instrumental, natural and personal
   B. Systematic only
   C. Random only
   D. Gross and compensating
   Answer: A. The answer groups errors into instrumental, natural and personal. (Key point: Classification)

2. What is the collimation error and how is it removed?
   A. Parallax; removed by focusing
   B. Line of collimation not parallel to the bubble tube axis; removed by balancing sights or two-peg adjustment
   C. Staff not vertical; removed by waving
   D. Bubble not centred; removed by foot screws
   Answer: B. It is an instrumental error cancelled by equal BS/FS distances or permanently adjusted. (Key point: Collimation error)

3. How do curvature and refraction affect staff readings?
   A. Curvature makes readings too low; refraction too high
   B. Both make readings too high
   C. Curvature makes readings too high; refraction makes them too low (1/7 of curvature)
   D. Both make readings too low
   Answer: C. Curvature Cc = 0.0785 d^2 raises the reading; refraction Cr = Cc/7 bends the ray down so reading is lower. (Key point: Curvature and refraction)

4. Which is a personal error?
   A. Bent staff
   B. Curvature of the earth
   C. Heat shimmer
   D. Staff not held on the same point at a change point
   Answer: D. Handling errors by the surveyor or staff holder are personal; bent staff is instrumental and the others natural. (Key point: Personal error)

## Related in Surveying I

- [Reciprocal levelling: RL of A, B at 1160.18 m](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Areciprocal-leveling-rl-b-1160-18) — Surveying I, chapter 5, asked 2×
- [Reciprocal levelling: RL of A, B at 1260.18 m](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Areciprocal-leveling-rl-b-1260-18) — Surveying I, chapter 5, asked 2×
- [Reciprocal levelling across river, 250 m](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Areciprocal-leveling-river-250m-eyepiece-height) — Surveying I, chapter 5
- [Reciprocal levelling AB 250 m, RL 1450.500](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Areciprocal-leveling-ab-250m-1-252) — Surveying I, chapter 5

## Related in other subjects

- [Types and sources of measurement errors](https://www.bctengineer.com/question.md?key=semester_3%2Fmetrology%3Atypes-sources-of-errors) — Metrology, chapter 2