Gauge pressure

From GAWDAwiki

Gauge pressure is the pressure relative to atmospheric pressure.^[1]The reading on a gauge, which is the difference between two pressures, is known as the gauge pressure. If the lower of the pressures is the pressure of the atmosphere, the total, or absolute, pressure is the sum of the gauge and atmospheric pressures.^[2]

References

1. http://www.bocindustrial.co.uk/bocindustrial/technical/glossary/a.asp
2. http://www.britannica.com/EBchecked/topic/227019/gauge-pressure