Surface weather analysis United States, temperature and dewpoint are plotted in degrees Celsius. The wind barb points in the direction from which the wind is coming. Each full flag on the wind barb represents of wind, each half flag represents . When winds reach , a filled in triangle is used for each of wind. In the United States, rainfall plotted in the corner of the station model are in inches. The international standard rainfall measurement unit is the millimeter. Once a map has a field of station models plotted, the analyzing isobars (lines of equal pressure), isallobars (lines of equal pressure change),
Alveolar pressure Alveolar pressure Alveolar pressure (P) is the pressure of air inside the lung alveoli. When the glottis is opened and no air is flowing into or out of the lungs, alveolar pressure is equal (zero cmH2O). During inspiration, the increased volume of alveoli as a result of lung expansion decrease the intra-alveolar pressure to a value below atmospheric pressure about -1 cmH2O. This slight negative pressure is enough to move 500 ml of air into the lungs in 2 seconds required for inspiration. At the end of inspiration, the alveolar pressure returns to atmospheric pressure (zero cmH2O). During expiration, the