Instrumental errors are those which arise due to faulty adjustment of instrument e.g pivot being bent, blunt pivot point etc. Variation in declination, magnetic changes in atmosphere due to clouds and Stromâ??s etc also comes under natural errors in compass surveying. 

Local attraction is term used to denote any influence which prevents needle from pointing to north in a given locality. 

 In chain and compass traversing, magnetic bearings of survey lines are measured by a compass and lengths of lines are measured eir with a chain or with a tape.

Compass surveying is not recommended for areas where local attraction is suspected due to presence of magnetic substance like steel structures, iron ore de, electric cables conveying currents.

Instrumental errors are those which arise due to faulty adjustment of instruments. They may be due to following reasons needle not being perfectly straight, sluggish needle etc.

 Compass traversing, lengths of lines are measured by a chain and magnetic bearings are measured by compass.

Compass surveying is recommended when area is large, undulating and crowded with many details. It is not recommended for areas where local attraction is suspected due to presence of a magnetic substance.

The errors may be classified as instrumental errors, personal errors, errors due to natural causes. Surveyor errors may come under personal errors.

Natural errors are those which are not in over hands or control to adjust. Variation in declination, magnetic changes in atmosphere due to clouds and Stromâ??s etc are some of examples of natural causes.

The magnetic bearings of traverse lines are measured by a odolite fitted with a compass. The direction of magnetic meridian is not established at each station but, magnetic bearings of lines are measured with a reference so direction of magnetic meridian established at first station.