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Pressure can be measured in bars in which 1 bar is equal to the atmospheric pressure at sea level and 14.5 PSI, which stands for Pounds per Square Inch. A milibar, or mbar, is 1/1000th of a bar. The pressure unit, mmwc, stands for millimeters per water column, and 1 mmwc = 9.8*10-5 bar = 9.8*10-8 mbar = 0.0014 PSI = 0.0098 mPa. Pascal (Pa) is the SI unit for pressure, and 1 mPa is 1/1000th of a Pa.