Linear measurements involve measuring horizontal distances using various direct, optical, and electronic methods. Common instruments for linear measurement include chains, tapes, arrows, ranging rods, offset rods, and marking pins. Chains available in metric units of 5, 10, and 30 meters typically have brass tallies every 1 meter. Tapes are more accurate and come in cloth, metallic, steel, invar, and fiberglass varieties. Cloth tapes are not durable or accurate while metallic tapes are flexible and durable due to interwoven brass, copper or bronze wires. Marking pins are 15 cm steel wires bent into rings used to mark points along chains.

2. LINEAR MEASUREMENT
Linear measurements are carried out for finding out
measurements in horizontal plane.
Various method of making liner measurements
are -
1. Direct methods
2. Optical methods
3. Electronic method

3. INSTRUMENTS FOR CHAINING :
Following Instruments are Commonly used in chaining :
(a) Chain (b) Tape (c) Arrows
(d) Pags (e) Ranging rods (f) Ranging poles
(g) Offset rods (h) Piumb bob (i) Whites
(j) Laths.

4. After the introduction of
metric unit in india the
metric chains are widely
used.
They are generally
available in length of 5,10,
and 30 metres.
Normally, this chain consists of galvanized mild steel wire of 4 mm diametar
known as link.
In case of 5 m and 10 m chains, brass tallies are provided at every 1 m.

5. Tapes are used for more accurate measurements of length .
Depending upon the material used, tapes are classified as -
1. Cloth or linen
tape
2.Metallic tape
3.Steel tape
4.Invar tape
5.Fibre glass tape

6. Cloth tape are made of woven linen, 12 mm to 15 mm wide, varnished to resist
motisture.
They are light in weight and flexible.
A cloth tape is rarely used for making accurate measurements, because of the
following reasons :
1. It is easily affeected by moisture and thus shrinks.
2. Its lingth gets altered by stretching.
3. It is likely to twist and tangle.
4. It is not strong and durable.

7. A metallic tape is made of varnished strip of waterproof linen interwoven with
small brass, copper or bronze wires.
They are light and flexible and not easily broken.
They are more durable as compared to cloth tape.

8. They are also known as marking pins .
They are used with chain for marking the
end of each chain.
They are made of steel wire 4 mm
diameter and the other is bent into
ring as shown in fig.

9. They are 15 cm long and 2.5 cm square in section.
One end of the peg is tapered to drive it into
ground.
As shown in fig 3.7 Wooden pegs are used for
marking the positions of stations. Biggersize
wooden pegs are also available for use in soft
ground(40 to 60 cmlong and 4 to 5 cm square)
Iron pegs are also available in 1 cm diameter.