PSIA
PSIA stands for pounds per square inch absolute. It is a unit of pressure measurement that includes atmospheric pressure in its calculation. Unlike PSIG (pounds per square inch gauge), which measures pressure relative to atmospheric pressure, PSIA measures the total pressure, including the atmospheric pressure at sea level (14.7 psi at standard atmospheric conditions). For example, if a vacuum reads 0 PSIA, it means it has no pressure at all, while 14.7 PSIA would be the normal air pressure at sea level.
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