Ranging:

Ranging is essential step in chain surveying to ensure that measurements are made in a straight path along the survey line. If the end stations are inter-visible, direct ranging can be resorted.

Ranging by Vision

Direct ranging by vision alone is done by stretching the tape or chain approximately along the survey line AB as in Figure. At least two persons are included in chaining and ranging. One surveyor known as follower is stationed behind beginning station A at the end of chain, while the other one called leader is situated at the distance of equal to or less than the chain length from A, carry the other ranging rod at an arms length from the body (position L in Figure). Follower, situated behind A directs leader to align ranging rod L along line AB. If the distance AL is large then sign language could be used in giving and following the directions. While L is perfectly aligned to exactly lie along sight line AB, the intermediate station L is fixed through driving the ranging rod or wooden peg in ground at correct position.

Figure: Ranging by Sight/Vision