The total pressure measured from absolute zero (i.e. from an absolute vacuum. (Absolute Pressure = Gauge Pressure + Atmospheric Pressure
Pabs = Prel + Patm). It is measured in psi(a), kPa(a), MPa(a), Bar(a), kg/cm2(a).
Changes in atmospheric pressure don’t affect absolute pressure. Absolute pressure cannot be negative. It is measured by using a manometer or barometer.
The primary difference between gauge pressure and absolute pressure is that the former uses atmospheric pressure as its zero points and the latter uses the absolute zero pressure as a reference.
In gauge pressure, the values change instantaneously with respect to the change in the ambient pressure. Additionally, the pressure differences below the sea level and at a substantial height should also be taken into consideration. In absolute pressure, every value is derived by measure the relative pressure with respect to that of the ideal vacuum and is independent of altitude, depth, or weather.
