Enlist the sources of error in chaining and state the precautions to be taken against error.

Enlist the sources of error in chaining and state the precautions to be taken against error.
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1 Answer

Answer :

In general, the distance measurement obtained in the field will be in error. Errors in the distance measurement can arise from a number of sources:

1. Instrument errors:

A chain may be faulty due to a defect in its manufacturing.

2. Natural errors.

The actual horizontal distance between the ends of the chain can vary due to the effects of

temperature,

elongation due to tension

sagging.

3. Personal errors.

 Errors will arise from carelessness by the survey crew:

1. poor alignment

2. faulty reading on the chain

Precautions:

Displacement of arrows: When the arrow is displaced, it may not be replaced accurately. To guard against this mistake, the end of each chain length should be marked both by the arrow and by a cross (+) scratched on the ground.

Failure to observe the position of the zero point of the tape: The chainmen should see whether it is at the end of the ring or on the tape.

Adding or omitting a full chain length (due to wrong counting or loss of arrows): This is the most serious mistake and should be guarded against. This is not likely to occur, if the leader has the full number (ten) of arrows at the commencement of chaining and both the leader and follower count them at each transfer. A whole chain length may be dropped, if the follower fails to pick up the arrow at the point of beginning.

Reading from the wrong end of the chain: e.g. reading 10 m for 20 m in a 30 m chain, or reading in the wrong direction from a tally, e.g. reading 9.6 m for 10.4 m. The common mistake in reading a chain is to confuse 10 m tag with 20 m tag. It should be avoided by noticing the 15 m tag.


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