The scale range must be chosen so that the measured process pressure is between 1/3 and 2/3 of the scale range. In this area the gauge reaches its highest accuracy. As a rule of thumb you can say that the measurement range should be two times larger than the operating pressure.
Choosing a too small measurement range will result in a pressure gauge which is always working in the last third of his scale. This can lead to metal fatigue of the pressure-responsive element because it is under constant high stress. Occasional overpressure is another reason for not choosing a too small measuring range.
The choice of a too large measuring range will in turn lead to an indication within the first third of the scale, where the accuracy is reduced.
Ensuring a working pressure between 1/3 and 2/3 of the scale range has the effect that pressure gauges according to ASME B40:100 or EN837, will reach their highest measurement accuracy. It also ensures a longer life of the pressure gauge, especially when the process is subject to cyclic pressures.
