HIM automatic and conventional measuring technology for the determination of air pressure
In addition to temperature, air pressure is one of the oldest variables measured in meteorology. Pressure is a force related to a unit area. The unit of pressure is therefore the (unit of force) / (unit of area), i. H. in the MBS system N / m2 or Pa (Pascal).
Since this pressure unit is very small, the unit is used in meteorology hPa
(hectoPascal: 1 hPa = 100 Pa).
There are also historical reasons for this, as the figures in hPa agree with the figures given in mbar, which have been valid for decades in meteorology.
Besides there was, from the main air pressure gauge, the mercury barometer, the unit derived 1 Torr. 1 Torr is the pressure of a mercury column 1 mm high, corrected to a mercury temperature of 0 ° C and to the standard severity (45 ° width, sea level).
The conversion is therefore based on the relationship:
(1) 1 • 103m • 13595 kgm3 • 9.806 m • s2 = 1 torr = 133.32 N • m2 = 1.3332 hPa
Sometimes you can find mm Hg (= mm of mercury) instead of the exact name Torr. At low pressure (dynamic pressure) you can still find the statement mm WS (= mm water column) = 9,806 N-m "2 -0.1 hPa. The units mbar, Torr, mm Hg and mm WS may not be used since 1978.