# What shall be the back bearing of a line, if its fore bearing is 280 degree?

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What shall be the back bearing of a line, if its fore bearing is 280 degree?
1. 80 degree
2. 100 degree
3. 190 degree
4. 200 degree

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Correct Answer - Option 2 : 100 degree

Concept:

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°.

Calculation:

Given,

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