Definition - What does Gauge Pressure mean?
Gauge Pressure is the additional pressure in any system that is relative to the atmospheric pressure. It is zero-referenced against the ambient air pressure and is equal to the difference between the absolute and atmospheric pressure. The negative signs are generally omitted and for distinguishing the negative pressure, a value can be affixed with the word “vacuum” and gauge can be characterized as vacuum gauge. Most of the tools that measure pressure give the pressure of system with regard to Gauge Pressure and opposed to the absolute pressure.
Petropedia explains Gauge Pressure
Gauge Pressure is considered as the most favorable pressure measurement for many practical applications. Absolute pressure is important for many pressure calculations; hence the atmospheric pressure should be added to gauge pressure for the calculations. The changes in atmospheric pressure because of the altitude or weather conditions influence the output of Gauge Pressure directly. For most of the working fluids in which fluids exist in a closed system, the Gauge Pressure measurements dominate. The Gauge Pressure is referred to as the positive pressure when it is higher than the ambient pressure and a vacuum or negative gauge pressure if it is lower than the atmospheric pressure.