Mm Hg from Torricelli experiment. The principle is based on mercury Generated static pressure To balance atmospheric pressure p， Therefore, the height of the mercury column can measure the atmospheric pressure In laboratory and meteorological measurement, millimeter mercury (mmHg) is usually used as the unit of atmospheric pressure
Except for large pressure The unit is also used for high vacuum engineering (especially in the environment where the pressure is low to the point where the viscosity disappears), blood pressure measurement Intraocular pressure Measurement, etc. according to Liquid pressure and Torricelli experiment The height of the mercury column shall be recorded when the pressure generated by the liquid level difference of the mercury column is in balance with the atmospheric pressure. according to pressure Calculation method: p=ρ gh ρ refers to mercury density (Unit: kg/m3)
G refers to gravity Ratio (in N/kg)
H refers to difference (Unit: m)
Changing h to mm is mmHg pressure The value of p is Pa Unit pressure Torricelli The liquid level difference measured at that time was 760mm, that is Atmospheric pressure 760mmHg Standard atmospheric pressure (1.013X10 ^ 5 Pa) can be converted as follows: P=1.013X10 ^ 5 Pa=760mmHg or 100 kPa=1000 Millibar ≈ 3/4m Mercury Column height The accurate conversion is 1mmHg=20265/152 ≈ 133.32236842105 Pa. And 1 mm Hg is converted into water column L=10.34m/760=0.013605m
Simultaneous mmHg and Bracket (Torr) Equivalent, and none of them is International System of Units Company members, Pascal Is the pressure International unit 。 
