Question

For no error in the magnitude, the difference (degree)in the magnitude of the fore bearing and back bearing of any line is ______

Answer 1

(b)
$\bullet$ If the difference between fore and back bearing is ${180}^0$, then both the end stations are considered to be free from local attractions, provided the compass is not having any instrumental errors.
$\bullet$ If the difference is not ${180}^0$, the discrepancy introduced may be because of
1. An error in observation of either fore or back bearing or both
2. Presence of local attraction at either or both of the stations