Offset Rod in Surveying

The following instruments are required for measurements with chain and tape:
(i) Arrows
(ii) Pegs
(iii) Ranging rods and ranging poles
(iv) Offset rods
(v) Laths
(vi) Whites
(vii) Plumb bobs and
(viii) Line ranger.

Arrows
When the length of the line to be measured is more than a chain length, there is need to mark the end of the chain length. Arrows are used for this purpose. A typical arrow is shown in Fig. 12.5. Arrows are made up of 4 mm diametered steel wire with one end sharpened and other end bent into a loop. Length of an arrow is approximately 400 mm.

Pegs
Wooden pegs are used in measuring a length of a line to mark the end points of the line. The pegs are made of hard wood of 25 mm × 25 mm section, 150 mm long with one end tapered as shown in Fig. 12.6. When driven in ground to mark station points they project about 40 mm.

Ranging Rods and Ranging Poles
For ranging intermediate points along the line to be measured, ranging rods and ranging poles are used.
Ranging rods are 2 to 3 m long and are made of hard wood. They are provided with iron shoe at one end as shown in Fig. 12.7.
They are usually circular in section with 30 mm diameter and are painted with 200 mm colour bands of red and white or with black and white. If distance is more than 200 m, for clear visibility they may be provided with multicoloured flags at their top. The ranging rods are occasionally used to measure
short distances since they are painted with alternate colour of band 200 mm.
Ranging poles are similar to ranging rods except that they are longer. Their length varies from 4 m to 8 m and diameter from 60 mm to 100 mm. They are made of hard wood or steel. They are fixed in the ground by making 0.5 m holes and then packed to keep them vertical.