Local attraction: AB 69°30′ compass traverse

The differences FB − BB are 183°00′, 178°30′, 177°15′, 182°00′ and 181°45′, so none of the lines is free from local attraction and all stations A, B, C, D, E are suspected. The included-angle method is used.

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

Step 2: Included (interior) angles

The included angle at a station uses the FB of the line leaving it and the BB of the line arriving at it, both observed at the same station, so local attraction cancels in the angle.

The sum of the interior angles should be $(2n-4)\times 90^\circ = 540^\circ$.

Sum observed = 537°30′; error = −2°30′; correction per angle = +0°30′ (equal distribution, since each angle is measured with the same care).

No line has FB − BB = 180°. Line BC has the smallest difference (−1°30′), so it is the most reliable; its adopted bearing is the mean of the FB and (BB ± 180°) = 192°15′.

Step 3: Corrected bearings from the corrected angles

Rule used: FB of next line = BB of previous line − interior angle (traverse run clockwise). Starting from BC = 192°15′ (BB 12°15′): CD = 12°15′ − 143°15′ + 360° = 229°00′, and so on round the traverse.

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

Interior angles from the corrected bearings

Sum = 540°00′ (as required).

Answer: Corrected bearings (FB): AB = 67°45′, BC = 192°15′, CD = 229°00′, DE = 258°15′, EA = 29°15′.