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Atmospheric pressure, sometimes also called barometric pressure, is the pressure within the atmosphere of Earth. In most circumstances atmospheric pressure is closely approximated by the hydrostatic pressure caused by the weight of air above the measurement point. As elevation increases, there is less overlying atmospheric mass, so that atmospheric pressure decreases with increasing elevation. Pressure measures force per unit area, with SI units of Pascals. On average, a column of air with a cross-sectional area of 1 square centimetre (cm2), measured from mean (average) sea level to the top of Earth's atmosphere, has a mass of about 1.03 kilogram and exerts a force or "weight" of about 10.1 newtons or 2.37 lbf, resulting in a pressure at sea level of about 10.1 N/cm2 or 101 kN/m2. A column of air with a cross-sectional area of 1 in2 would have a mass of about 6.65 kg and a weight of about 65.4 N or 14.7 lbf, resulting in a pressure of 10.1 N/cm2 or 14.7 lbf/in2.
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  • Mean sea-level pressure 

  • Surface pressure 

  • Altitude variation 

  • Local variation 

  • Records 

  • Measurement based on depth of water 

  • Boiling point of water 

  • Measurement and maps