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The following bearing observed in the area where local attraction was suspected determine the correct magnetic bearing if the declination is 3$^\circ$30' east.
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Line FB BB Declination
PQ 220$^\circ$30' 41$^\circ$15' 3$^\circ$30'E
QR 260$^\circ$45' 79$^\circ$30' 3$^\circ$30'E
RS 19$^\circ$30' 200$^\circ$ 3$^\circ$30'E
SP 100$^\circ$ 280$^\circ$ 3$^\circ$30'E

The difference of BB and FB of SP is 180O hence station S and P free from local attraction

  1. FB of PQ= 220$^\circ$30’, BB Of PQ= 41$^\circ$15’

    FB-BB= 220$^\circ$30’ - 41$^\circ$15’= 180$^\circ$

  2. Observed BB of PQ= 220$^\circ$30’

    Correct BB of PQ=220$^\circ$30’- 180$^\circ$=40$^\circ$30’

    Observed BB of PQ is 41$^\circ$15’

    Error is 40$^\circ$30’- 41$^\circ$15’ = - 0$^\circ$45’

  3. Observed FB of QR is = 260$^\circ$45’

    Correct FB of QR= 260$^\circ$45’ - 0$^\circ$45’= 260$^\circ$0’

    Correct BB of QR =260$^\circ$0’- 180$^\circ$= 80$^\circ$

    Observed FB of QR=79$^\circ$30’

    Error is 80$^\circ$ - 79$^\circ$30’ = 0$^\circ$30’

  4. Observed BB of RS = 19$^\circ$30’

    Correct BB of RS= 19$^\circ$30’ + 0$^\circ$30’=20$^\circ$00’

    Correct FB of RS = 20$^\circ$00’ - 180$^\circ$=200$^\circ$00’

Line Declination Corrected True bearing
FB BB FB BB
PQ 3$^\circ$30'E 220$^\circ$30' 40$^\circ$30' 224$^\circ$ 44$^\circ$
QR 3$^\circ$30'E 260$^\circ$ 80$^\circ$ 263$^\circ$30' 83$^\circ$30'
RS 3$^\circ$30'E 20$^\circ$ 200$^\circ$ 23$^\circ$30' 203$^\circ$30'
SP 3$^\circ$30'E 100$^\circ$ 280$^\circ$ 103$^\circ$30' 283$^\circ$30'
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