Observational Errors:

Even when the instrument is in perfect order, some errors may occur during bearing measurements. These could be because of

(a) Setting and levelling inaccuracies, i.e. the compass center may not coincide the center point of survey station, or it may not be levelled accurately so that it does not lie in a horizontal plane.

(b) Ranging inaccuracies, i.e. the ranging rods at other object stations may not be fixed in vertical position or these may not be perfectly bisected by line of sight.

(c) Reading and recording inaccuracies, i.e. due to carelessness, the position of line of sight may either be not read properly or accurately or wrongly recorded in field notebook.