Proper calibration of gauges is important to ensure measurements are accurate. Whether the gauge measures pressure, vacuum, temperature or rpm, the calibration procedure is fundamentally the same. Accuracy is verified by testing the gauge at its minimum point, at full-scale or span and throughout its range, called linearity.
All gauges are designed to read from a minimum to a maximum value accurately. The minimum is often zero and represents no input. The zero can usually be adjusted with a front panel screw.
The span of a gauge is its full-scale point. Span corrections are made by internal adjustment of the segment tail on the gauge meter movement.
After the zero and span are correct, the linearity is verified. This is done by testing several points along the scale. If corrections are needed, the linkage of the gauge movement can be adjusted. Span and linearity adjustments are often interactive, so several repetitions may be needed.
