---
title: "Local attraction, bearings AB 305°00′ (EA 45°)"
subject: "Surveying I"
chapter: 4
key: "semester_3/surveying_i:local-attraction-ea-305-00"
source: https://www.bctengineer.com/q/semester_3/surveying_i/local-attraction-ea-305-00
site: BCT Engineering
---

# Local attraction, bearings AB 305°00′ (EA 45°)

Surveying I · Chapter 4: The Compass

- Asked in: 2070 Chaitra (old course), 10 marks
- Video: [local attraction problem in surveying || compass survey|| survey engineering|| #local_attraction](https://www.youtube.com/watch?v=i_3QTIOjHek) — Aim 2 Civil Class
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/surveying_i/local-attraction-ea-305-00
- Whole chapter: https://www.bctengineer.com/md/semester_3/surveying_i/chapter-4

## Question

The following bearings were observed in a compass traverse.

| Line | AB | BC | CD | DE | EA |
|---|---|---|---|---|---|
| FB | 305°00′ | 75°30′ | 115°30′ | 166°30′ | 225°00′ |
| BB | 125°30′ | 254°30′ | 297°30′ | 345°00′ | 45°00′ |

At what stations do you suspect local attraction? Find the correct bearings of all the lines.

## Short answer

Line EA has FB−BB=180°, so stations E and A are free. Correcting sequentially: AB 305°00′ is correct, then B correction −0°30′ gives BC 75°00′, C correction +0°30′ gives CD 116°00′, D correction −1°30′ gives DE 165°00′. Corrected bearings: AB 305°00′, BC 75°00′, CD 116°00′, DE 165°00′, EA 225°00′.

## Answer

Differences FB − BB: AB 179°30′, BC 181°00′, CD 178°00′, DE 181°30′, EA 180°00′. Line EA is free of attraction, so stations E and A are free; the other stations B, C and D are suspected.

Local attraction at a station is detected by comparing the fore bearing (FB) and back bearing (BB) of each line: if there is no local attraction at either end, $\text{FB} - \text{BB} = 180^\circ$ exactly.

#### Step 1: Check each line

| Line | FB | BB | FB − BB | Remark |
|---|---|---|---|---|
| AB | 305°00′ | 125°30′ | 179°30′ | Differs by −0°30′ |
| BC | 75°30′ | 254°30′ | 181°00′ | Differs by +1°00′ |
| CD | 115°30′ | 297°30′ | 178°00′ | Differs by −2°00′ |
| DE | 166°30′ | 345°00′ | 181°30′ | Differs by +1°30′ |
| EA | 225°00′ | 45°00′ | 180°00′ | Free, difference = 180° |

Line EA has a difference of exactly 180°, so stations E and A are free from local attraction. The other stations are corrected one after another, starting from A.

#### Step 2: Correct the stations in turn

- Line AB: FB at A = 305°00′ is correct. The correct BB is 125°00′, observed 125°30′, so the correction at B is −0°30′.
- Line BC: FB at B = 75°30′ with correction −0°30′ gives 75°00′. The correct BB is 255°00′, observed 254°30′, so the correction at C is +0°30′.
- Line CD: FB at C = 115°30′ with correction +0°30′ gives 116°00′. The correct BB is 296°00′, observed 297°30′, so the correction at D is −1°30′.
- Line DE (check): FB at D = 166°30′ with correction −1°30′ gives 165°00′. The correct BB is 345°00′, which equals the observed value, so E needs no correction, as expected.

| Station | A | B | C | D | E |
|---|---|---|---|---|---|
| Correction | 0 | −0°30′ | +0°30′ | −1°30′ | 0 |

Stations affected by local attraction: B, C, D.

#### Step 3: Corrected bearings

| Line | Observed FB | Correction | Corrected FB | Observed BB | Corrected BB |
|---|---|---|---|---|---|
| AB | 305°00′ | 0 | 305°00′ | 125°30′ | 125°00′ |
| BC | 75°30′ | −0°30′ | 75°00′ | 254°30′ | 255°00′ |
| CD | 115°30′ | +0°30′ | 116°00′ | 297°30′ | 296°00′ |
| DE | 166°30′ | −1°30′ | 165°00′ | 345°00′ | 345°00′ |
| EA | 225°00′ | 0 | 225°00′ | 45°00′ | 45°00′ |

Check: corrected FB − corrected BB = 180° for every line.

**Answer:** Corrected bearings (FB): AB = 305°00′, BC = 75°00′, CD = 116°00′, DE = 165°00′, EA = 225°00′.

## Check yourself

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

1. Line EA has FB - BB = 180°. Which stations are suspected of local attraction?
   A. A, B and C
   B. B, C and D
   C. Only E and A
   D. C, D and E
   Answer: B. EA is exactly 180°, so E and A are free; the remaining stations B, C and D are suspected. (Key point: Free and suspected stations)

2. FB at A (305°00′) is correct. The correct BB of AB should be 125°00′ but 125°30′ was observed. What is the correction at B?
   A. -0°30′
   B. +0°30′
   C. -1°30′
   D. 0
   Answer: A. Correction = correct BB - observed BB = 125°00′ - 125°30′ = -0°30′. (Key point: Correction at B)

3. After correcting B, FB of BC = 75°30′ - 0°30′ = 75°00′, so correct BB of BC is 255°00′ (observed 254°30′). What is the correction at C?
   A. -0°30′
   B. +1°00′
   C. +0°30′
   D. -1°30′
   Answer: C. Correction at C = 255°00′ - 254°30′ = +0°30′; corrections are carried station by station. (Key point: Correction at C)

## Close variants set in other exams

- [Local attraction, bearings AB 305°30′](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ea-bb-44-00) — Surveying I, chapter 4, asked 2×

## Related in Surveying I

- [Local attraction: AB 69°30′ compass traverse](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ab-69-30-reordered) — Surveying I, chapter 4
- [Local attraction, BC 79°30′ and DE 82°15′](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-ab-191-30-bc-79-30) — Surveying I, chapter 4
- [Local attraction and true bearings, 1°30′E](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Acompass-closed-traverse-declination-1-30-east) — Surveying I, chapter 4
- [Local attraction and true bearings, 7°W](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-true-bearings-7w) — Surveying I, chapter 4
- [Local attraction, S 40°30′ W traverse](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-quadrantal-s40-30w) — Surveying I, chapter 4
- [Local attraction with quadrantal bearings](https://www.bctengineer.com/question.md?key=semester_3%2Fsurveying_i%3Alocal-attraction-quadrantal-bearings-s11-30w) — Surveying I, chapter 4

## Related in other subjects

- [Bearings of DE and EA in traverse ABCDE](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-abcde-bearings-de-ea) — Surveying II, chapter 1, asked 2×
- [Bearings of BC and CD in traverse ABCDE](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-abcde-bearings-bc-cd) — Surveying II, chapter 1, asked 2×
- [Missing bearings of BC and DE in traverse](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Atraverse-missing-bearings-bc-de) — Surveying II, chapter 1
- [Closed traverse missing EA bearing, BC length](https://www.bctengineer.com/question.md?key=semester_4%2Fsurveying_ii%3Aclosed-traverse-abcdea-missing-ea-bc) — Surveying II, chapter 1