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Instrument for measuring the condition of a fluid (liquid or gas) that is specified by the force the fluid would apply, when at rest, to a unit area, such as pounds per square inch (psi) or pascals (Pa). The reading on the gauge, called the gauge pressure, is always the difference between two pressures. When the lower of the pressures is that of the atmosphere, the total (or absolute) pressure is the sum of the gauge and atmospheric pressures.
This entry comes from Encyclopædia Britannica Concise. For the full entry on pressure gauge, visit Britannica.com.