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In a region with magnetic declination of 2°E, the magnetic Fore bearing (FB) of a line AB was measured as N79°50’E. There was local attraction at A. TO determined the correct magnetic bearing of the line, a point O was selected at which there was no local attraction. The magnetic FB of line AO and OA were observed to be S52° 40’E and N50°20’W, respectively. What is the true FB of line AB?


1. N81°50’E
2. N82°10’E
3. N84°10’E
4. N77°50’E

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Correct Answer - Option 3 : N84°10’E

Magnetic Declination, δ =2°E

Magnetic FB of AB = N 79°50’E

To find local attraction at station A

As station O is free from local attraction

Hence FB of OA will be correct

Correct FB of OA = N 50°20’W @ 309° 40’

∴ Correct BB of OA = @ 309° 40’ - 180° = 129° 40’

∵ Observed FB of AO= Observed BB of OA= S52° 40’E= 127°20’

Error = MB – TB = 127° 20’ – 129° 40’ = - 2° 20’

Correction = + 2° 20’

Local attraction at station A

= + 2°20’ @   2°20’ E

∴ Magnetic F.B of AB = N 79° 50’ E

δ = 2° E and local attraction = 2° 20’E

∴ True Bearing of FB of AB = 79° 50’ + 2° 20’ + 2° = N84° 10’E

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