Sources of Error:

Several errors observed during a compass survey could be widely classified as Instrumental errors, Observational errors and External influences.

Instrumental Errors

These could be due to defective manufacture or due to damage to instrument during rough handling, transportation and use. For instance,

(a) The needle might not be perfectly straight or balanced.

(b) Needle loosing their magnetic property.

(c) The pivot might become blunt or bent.

(d) The plane of sight loosing its verticality and/or twisted so that it is not passing through the centre of compass.

(e) The graduated circle may loose its shape or horizontality.