Absolute pressure refers to the pressure directly acting on the surface of a container or object, that is, the actual pressure borne by the object. Its zero point is absolute vacuum, and the symbol is PABS (ABS is subscript). The pressure exerted by a thick layer of atmosphere surrounding the Earth’s surface on the Earth’s surface or surface objects is called “atmospheric pressure”, with the symbol B.
There are three ways to express pressure, namely: absolute pressure, gauge pressure, negative pressure, or vacuum degree.
(1) Absolute pressure is the actual pressure that an object is subjected to, and its zero point is absolute vacuum.
(2) Gauge pressure refers to the difference between absolute pressure and atmospheric pressure.
(3) Vacuum degree refers to the absolute value of the negative pressure value when the gauge pressure is negative (i.e. negative pressure) when the absolute pressure value is less than atmospheric pressure.
The difference between an absolute pressure gauge and a vacuum gauge is the measurement reference, which is whether the zero scale is absolute vacuum or atmospheric pressure.