---
title: "Factors of closing error; graphical adjustment"
subject: "Surveying I"
chapter: 4
key: "semester_3/surveying_i:closing-error-factors-graphical"
source: https://www.bctengineer.com/q/semester_3/surveying_i/closing-error-factors-graphical
site: BCT Engineering
---

# Factors of closing error; graphical adjustment

Surveying I · Chapter 4: The Compass

- Asked in: 2080 Baisakh, 1+3 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/closing-error-factors-graphical
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4

## Question

List out the factors causing closing error of compass traverse. Explain the graphical adjustment of closing error of plotting of compass traverse.

## Short answer

Closing error arises from mistakes in length, bearings, local attraction, plotting, or booking. For graphical adjustment by Bowditch's rule, draw a base line representing the perimeter; at its end erect a perpendicular equal to the closing error. Ordinates from cumulative station points on the base to the line from start to top give corrections applied parallel to the closing direction.

## Answer

#### Factors causing closing error in a compass traverse

1. Errors in **measured lengths** (incorrect tape length, slope not reduced, sag, wrong tension, miscounted chain lengths).
2. Errors in **observed bearings** (compass not centred or levelled, sticky needle, reading mistakes, parallax, wrong back-sight).
3. **Local attraction** at a station that has not been detected or corrected.
4. Errors in **plotting** (wrong scale, protractor error, thick pencil lines, shrinkage of paper).
5. **Booking and calculation mistakes** (wrong FB/BB recorded, wrong conversion).

#### Graphical adjustment of the closing error (Bowditch's rule)

The closing error is distributed so that the correction at a station is proportional to its cumulative distance from the starting point.

1. Plot the traverse A-B-C-D-E-A′; the closing error is the line A′A.
2. Draw a base line equal to the perimeter and mark the points b, c, d, e at the distances AB, AB+BC, AB+BC+CD, ... from A; the last point is A′.
3. At A′ draw a perpendicular A′X equal to the closing error (plan scale) and join AX.
4. Vertical ordinates from b, c, d, e to AX are the corrections for B, C, D, E.
5. On the plan, from each of B, C, D, E, draw a line parallel to A′A and set off the correction towards A. Join the new points to give the adjusted traverse.

```text
                                      X
                                    . |
                                .     |
                          . e'        |
                    . d'  |           |
              . c'  |     |           |
        . b'  |     |     |           |
 A -----b-----c-----d-----e-----------A'
 (base = perimeter, marks at cumulative distances;
  A'X = closing error, drawn at right angles)
```

## Check yourself

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

1. Which is a cause of closing error in compass traverse?
   A. Using a dry pencil
   B. Undetected local attraction
   C. The colour of the pegs
   D. The weather forecast
   Answer: B. Local attraction, length errors, bearing errors, plotting and booking mistakes cause closure errors. (Key point: Closing error factors)

2. In Bowditch's rule the correction at a station is proportional to:
   A. The angle at the station
   B. Its elevation
   C. Its cumulative distance from the start
   D. The number of stations only
   Answer: C. Corrections grow with distance travelled along the traverse. (Key point: Bowditch principle)

3. In the graphical adjustment the base line is drawn equal to:
   A. The closing error
   B. The longest side
   C. The first side
   D. The perimeter of the traverse
   Answer: D. Stations are marked on it at cumulative distances. (Key point: Graphical base line)

4. The perpendicular A'X at A' is made equal to:
   A. The closing error at plan scale
   B. The perimeter
   C. The longest correction
   D. Half the closing error
   Answer: A. Ordinates from AX give the corrections at each station. (Key point: Perpendicular)

## Related in Surveying I

- [Closing error; plotting methods in compass traverse](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aclosing-error-plotting-methods) — Surveying I, chapter 4
- [Closing error and graphical adjustment](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Aclosing-error-graphical-adjustment) — Surveying I, chapter 4, asked 13×
- [Two peg: closing error and precision of level](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Atwo-peg-cd-50m-e-mid-f-5m) — Surveying I, chapter 5