Correct Answer - Option 2 : 100 degree
We know the relationship between FB and BB
Back bearing (BB) = Fore bearing (FB) ± 180°.
+ve sign is used if FB is less than 180° and –ve sign is used if FB is more than 180°.
Fore Bearing of line = 280 °
∴ Back bearing = 280° – 180° = 100
- Whenever there is any station affected by local attraction, then the difference between the fore bearing and back bearing is not equal to 180°
- If the difference is exactly 180°, the two stations may be considered as not affected by local attraction
- If the difference is not 180°, better to go back to the previous station and check the fore bearing
- If that reading is the same as earlier, it may be concluded that there is a local attraction at one or both stations