Correct Answer - Option 2 : Always Subtractive
Concept:
Sag correction is given by:
\({C_s} = - \frac{{{{\left( {w L} \right)}^2}L}}{{24\;{P^2}}}\)
Where,
l = the length of the tape (in metres) suspended between supports
P = Pull applied in kg or N
W = weight of the tape in kg or N per metre run
Cs = Sag correction in metres for length (l)
wL = weight of tape suspended between the supports.
Therefore,
i) Sag correction is directly proportional to the square of the weight of the tape (kg per metre run)
ii) Sag correction is inversely proportional to the pull applied.
Sag correction is always negative
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Error due to
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Error
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Correction
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Standardization
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+ve or -ve
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-ve or +ve respectively
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Temperature
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+ve or -ve
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-ve or +ve respectively
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Pull
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+ve or -ve
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-ve or +ve respectively
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Slope
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Always +ve
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Always -ve
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Sagging
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Always +ve
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Always -ve
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Wrong Alignment
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Always +ve
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Always -ve
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