Millibar
The millibar (mb) is commonly used in meteorology. The millibar is a metric unit of pressure equivalent to 100 pascals. Standard Earth atmospheric pressure at sea level is approx 1013.25 millibars.
mm of water
The millimeter of water (mmH₂O) is a unit of pressure exerted by a 1 millimeter column of water at 4 degrees Celsius under standard gravity.