Offsets are taken perpendicular to survey lines. They are used to mark objects and lateral distance to m, using an offset rod.

There is no instrument like an optical staff. Optical square is an instrument which consists of circular box with three slits. Cross staff is a frame of box mounted on a pole. Prism square is an advanced version of an optical square. Site square consists of two telescopes set at 90os.

There can be 5 types of chains used for chain surveying. They are metric chain, Gunterâ??s chain, engineerâ??s chain, revenue chain and steel band or band chain.

Gunterâ??s chain is also called surveyorâ??s chain and is 66ft long. It consists of 100 links, each being 0.6 ft. Eighty Gunterâ??s chain corresponds to 1 mile.

Ranging is used to locate intermediate points. They are marked using ranging rods. It is done when a survey line is very long and marks are required to distinguish line.

The line joining main survey station is called main survey line. The biggest of main survey line is base line, and or features are plotted with respect to this line.

Chain surveying is suitable for a survey of small areas. The area is divided into well- conditioned triangles and triangulation is principle used. 

Ranging is of 2 types â?? direct and indirect. Direct ranging is done using a line ranger or naked eye. Indirect ranging is done when starting and ending points are not visible. 

Field book is used to enter all measurements done while surveying. It is an oblong book of size 20x12cm and opens length wise. 

The three types are open cross staff, French cross staff and adjustable cross staff. Open cross staff has two vertical, opposite slits. French cross staff consists of a hollow octagonal box. The adjustable cross staff consists of two cylinders of equal diameter, one placed on top of or.