Surveying and Levelling : STUDY OF CHAIN AND TAPE AND ACCESSORIES USED FOR CHAIN SURVEYING : Practical 3

 STUDY OF CHAIN AND TAPE AND ACCESSORIES USED FOR CHAIN

SURVEYING 

DESCRIPTION OF THE INSTRUMENTS:- 

A) Chain:- 

1. The chains are made in lengths of 30 meters/20 meters.

2. The brass tallies are fixed at every 5m length.

3. Small brass rings are provided at every one meter length.

4. It is composed of 100 or 150 pieces of galvanized mild steel wire of 4mm in 

diameter called links.

5. The ends of each links are bent into a loop and connected together by means of 3 

oval rings which give flexibility to the chain.

6. The length of each links is 20cm i.e. the distance between 2 consecutive middle 

rings.

7. The end of the chains is provided with brass handle for dragging the chain on the 

ground.

8. The chain length is measured from the outside of one handle to the other.

9. To hold the arrows in the position with the handle of the chain a groove is cut on 

the outside surface of the handle.

B) Ranging rods:- 

1. They are usually of 2m or 3m in length.

2. They are in circular cross section and having alternate black, white and red bands of 

20 cm length each to make them visible at a distance.

3. They are used for ranging the lines and for marking the positions of points on the 

ground.

C) Arrows:- 

1. They are made of a steel wire of 4mm diameter for 40cm length.

2. They are pointed at one end for inserting into the ground and bent at the other end 

for facility of carrying.

3. They are used to mark the end of each chain during chaining. 

D) Offset rods:- 

1. These are used for measuring rough offsets.

2. They are round rods with pointed end on one side and provided with notch or a 

hook at the other to facilitate pulling the pushing the chain through obstructions.

 

E) Cross staff:-

1. It consists of a wooden block with two fine sow cuts at right angles to each other on 

the top.

2. It is used to set a perpendicular at a given point on the chain line.

3. The head is fixed to a top of an iron staff with pointed end to drive into the ground. 

F) Optical square:- 

1. This is also used to set a perpendicular with more accuracy.

2. This has 2 mirrors placed at an angle of 45  ۨ to each other.

3. By means of reflection we can see the ranging rods along the chain line and the 

offset point at right angles to the chain lines simultaneously.