Errors in Chaining:
The main chaining errors that may occur May classified as
- Compensating Error
- Cumulative Error
These errors may be due to natural uses such as say variation in temperature, defects in construction and adjustment of the instrument, personal defects in vision etc.
Compensating Errors:
The compensating errors may occur in both direction and hence it tends to compensate i.e. the appearance may result too small or too large.
In chaining, these errors may be caused due to the following reasons:
- The incorrect holding of the chain.
- The follower may not bring his handle of the chain to the side of the arrow.
- Fractional parts of the chain or tape may not be correct if the total length of the chain is adjusted by insertion or removal or a few connection rings from one chain portion, or throughout its length, the tape is not calibrated uniformly.
- During stepping operation crude method of plumbing (such as dropping of stone from the end of the chain) is adopted.
- When chain angles are set out with a chain which is not uniformly adjusted or with a combination of chain and tape.
Cumulative Errors:
Those errors may occur in the same direction and tend to accumulate or add up. I.e. to make the measurement apparent always too short or too long.
Positive Errors:
(Making the measured lengths more than the actually )
- The length of the chain or tape is shorter than the standard, because of bending of links, removal of too many links in adjusting the length, knots in the connecting links, clogging of rings clay.
- The tape was calibrated the temperature was lower.
- The shrinkage of tape occurs when tape becoming wet.
- The slope correction is not applied to the length measured along the sloping ground.
- The correction of sag is not applied when the chain or tape may be suspended in air.
- Measurements are made along the incorrectly aligned line.
Negative Errors:
(Making the measured lengths less than the actual)
- The negative error is basically caused because of the chain or tape length greater than the standard limit, because of the flattening or wear of the connecting rings.
- The ring joints opening, the temperature was higher than the one at which the tap or chain was calibrated.
The linear final measurement error is basically composed of two main portions:
1. Cumulative errors: (error of marking)
2. Compensating: (Error due to incorrect length)
Mistakes in Chaining:
The mistakes are generally avoidable and cannot be classed under any law of probability.
Due to the inexperienced chainmen, the following mistakes may be made due to the following reasons.
1. Displacement of arrows.
2. Failure to observe the position of the zero points of the tape.
3. Adding or omitting a full chain or tape length.
4. Reading from the wrong end of the chain.
5. Reading numbers incorrectly.
6. Calling numbers wrongly.
7. Reading wrong meter marks.
8. Wrong booking.
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