While compass surveying, the magnetic needle is sometimes disturbed from its normal position under the influence of external attractive forces.
[1] The external forces are produced by sources of local attraction which may be current carrying wire (magnetic materials) or metal objects.
The iron made surveying instruments such as metric chains, ranging rods and arrows should also be kept at a safe distance apart from compass.
[3] Local attraction at a place can be detected by observing bearings from both ends of the line in the area.
[3] There are two common methods of correcting observed bearings of the lines taken in the area affected by Local Attraction.