The pressure gauge is an instrument for measuring the pressure of fluids or gases. … “Gauges” measuring depression are called vacuum gauge At the beginning the word “pressure gauge” was referred only to instruments with a liquid column, called U gauge.

Instruments used to measure and display pressure in an integral unit are calledpressure gauges or vacuum gauges. A manometer (not to be confused with nanometer) is a good example, as it uses a column of liquid to both measure and indicate pressure.

When the pressure inside the bourdon tube increases, the bourdon tube uncoils slightly. The amount of uncoiling that occurs is proportional to the pressure inside the bourdon tube. As the tube uncoils, its motion activates the gear and shaft system that turns the pointer on the gauge.