Ct = CL ( T – Ts )
Where: Ct = temperature correction
C = coefficient of linear expansion ( 0.0000116 per degree centigrade )
L= length of the tape or length measured
T= observed temperature
Ts = standard temperature ( 20 0C)
Correction Due to Sag (always subtract)
Sag- to bend or hang down in the middle especially because of the weight.
Sag shortens the horizontal distance between end graduations since the tapelength remains the same. Thus, when a stretched tape sags, the actual distance between the points is something less than the reading on the tape.
The magnitude of error due to sag depends on the weight of the tape, the unsupported length and the tension applied.
The correction due to sag is the difference in length between the arc formed by the tape and the subtending chord. In determining this correction, the arc is assumed to be a parabola, and is computed with sufficient precision by the formula:
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