Pressure is a measure of the total weight of the atmosphere above the level at which it is measured.
The conventional unit of pressure used by meteorologists is the millibar. Average sealevel pressure is about 1000.0 mb. But, typically, pressure can vary from about 960.0 mb to about 1050.0 mb. (Sealevel pressure in other units: 14 lbs/in2, 30.00 inches of mercury)
Pressure observations are coded and plotted around the station circle as described in class.
Although pressure at sealevel does not vary much from 1000 mb, these variations on a level surface account for wind.