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36
Note. If the polynomial equation is used it is important that the value of C, in the
polynomial equation, be taken in the field, following the procedures described in Section
2.5. The field value of C is calculated by inserting the initial field zero reading into the
polynomial equation with the pressure, P, set to zero.
If the field zero reading is not available, calculate C using the zero pressure reading on the
calibration sheet. In the above example, the value of C would be derived from the equation:
2
0 = A(8981)
+ B(8981) from which C = +1053
Equation 19 - Calculating C Using the Zero Pressure Reading from the Calibration Sheet
It should be noted that where changes of earth pressures are being monitored it makes little
difference whether the linear coefficient or the polynomial expression is used.
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