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How is standard atmospheric pressure expressed in millimetres of mercury?
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vacuum technology
Diagram of a McLeod gauge.
In the context of vacuum technology, standard atmospheric pressure is expressed as 760 millimetres of mercury (mm Hg).1
This measurement corresponds to the height of a vertical column of mercury supported by the pressure of the atmosphere at sea level. While this unit was historically common, the term "torr" was later introduced to represent 1 mm Hg, and the SI unit for pressure is now the pascal, with one standard atmosphere equal to 101,325 pascals.231