Tape Correction, Sag Correction and Pull Correction | Surveying and Levelling

Tape Correction, Sag Correction, Pull Correction and Temperature Correction

In this article, I will list out different formulas for the respective corrections…

Tape Correction

The following corrections are to be made for measurements taken with a tape because tape can never be practically used under specified standard conditions.

Correction for absolute length

Absolute length of tape is its actual length under specified condition

Ca = Lc/L

Where, Ca = correction to be applied to the tape in ‘m’

Lc = measured length in ‘m’

L = nominal length of tape in ‘m’

Correction for temperature

Length of tape is increased with the increase of temperature and decrease with decrease of temperature.

Ct = A (Tm – Ts)


A = coefficient of thermal expansion per one degree Kelvin

Tm = temperature during the measurement in Kelvin

Ts = temperature at which the tape standardised in Kelvin

Correction for Sag

When the tape is suspended from two ends in air

Sag correction, Cs = L/24(W/P)2

Where, L = horizontal distance between supports in meters

W = weight of tape in Newtons

P = Pull applied in Newtons

Correction for Pull

If the pull during measurement in not the same at which the tape is standardised then the correction for pull is necessary.

Cp = [(P – P0)/AE) * L]


P = pull in Newtons

L = length of measured line in ‘m’

P0 = standard pull in Newtons

E = Young’s Modulus in N/mm2

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