Corrected and true bearings, 8°40′E

Line DA has FB − BB = 180°00′, so stations D and A are free; B and C are suspected. Declination is 8°40′ East, so true bearing = magnetic bearing + 8°40′.

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 DA has a difference of exactly 180°, so stations D 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 = 66°15′ is correct. The correct BB is 246°15′, observed 244°00′, so the correction at B is +2°15′.
• Line BC: FB at B = 129°45′ with correction +2°15′ gives 132°00′. The correct BB is 312°00′, observed 313°00′, so the correction at C is −1°00′.
• Line CD (check): FB at C = 218°30′ with correction −1°00′ gives 217°30′. The correct BB is 37°30′, which equals the observed value, so D needs no correction, as expected.

Stations affected by local attraction: B, C.

Step 3: Corrected bearings

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

Answer: Corrected bearings: AB = 66°15′ / 246°15′, BC = 132°00′ / 312°00′, CD = 217°30′ / 37°30′, DA = 306°45′ / 126°45′ (FB / BB). True bearings (FB): AB = 74°55′, BC = 140°40′, CD = 226°10′, DA = 315°25′.