In presence of magnetic materials, the magnetic needle deviates from the magnetic meridian and thus provides wrong direction of a line. The deviation arising from such local sources is called local attraction. If the fore bearing and back bearing of a line does not differ by 180°, then there is a possibility of local attraction during the observation of the line. Otherwise, if the sum of the interior angles of a closed traverse does not provide (2n - 4) right angles [where n is the number of sides in the traverse], then there is a possibility of local attraction during the observation of the traverse.

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