Instruments and Procedures:
Compass
The compass essentially consists of a freely suspended magnetic needle mounted on a smooth pointed pivot. The needle could freely move over a graduated scale. Two slit vanes are provided on the frame - one as the object vane and other as eye vane - placed at 180o to provide the line of sight. A tripod stand is provided on which the compass can be mounted and positioned over the survey station, while taking observations.
A circular metal box, approximately 100 mm diameter, is used with a hardened steel pivot at the middle. The magnetic needle, graduated aluminium ring and vanes etc. are other parts of the compass. Design of these parts and their placement vary in different types of compass.
The two types of compass - prismatic compass and surveyors compass - are currently used in practice.