what is gauge pressure

Gauge pressure is the pressure of a system above atmospheric pressure. It is zero-referenced against ambient air (or atmospheric) pressure, so gauge pressure readings include the pressure from the weight of the atmosphere. Gauge pressure is positive for pressures above atmospheric pressure, and negative for pressures below it. Absolute pressure is the sum of gauge pressure and atmospheric pressure. Differential pressure is the difference in pressure between two points in a process. Gauge pressure is the most often used method of measuring pneumatic pressure.