There are several units to express atmospheric pressure as shown below: •In meteorology, the atmospheric pressure is expressed in bars and millibars. 1 bar = 106 dyne/cm2 = 105 Pa, 1 millibar =1000 dyne/cm2 •Another unit is torr, named after Torricelli. 1 torr = pressure of 1 mm of mercury = 133.42 Pa. •Atmospheric pressure is usually expressed as height of mercury column in cm or mm.