8.2.1.1 The spring shall be calibrated at room temperature
23 6 5°C (73.4 6 9°F) by applying successive increments of
force not exceeding 250 N (50 lbf) and measuring the
corresponding deflection to the nearest 0.2 mm (0.01 in.). The
curve obtained by plotting the forces against the corresponding
deflections shall have a slope of 70 6 3.5 kN/m (400 6 20
lbf/in.) at 1.8 kN (400 lbf). The slope is obtained by dividing
the two forces above and below 1.8 kN by the difference
between the corresponding deflections.