Atmospheric pressure and its measurement.

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Atmospheric pressure :

Atmospheric pressure, sometimes also called Barometric pressure, is the pressure with in the atmosphere of Earth (or that of another planet). In most circumstances atmospheric pressure is closely approximated by the hydro static 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. 

Unit :

Pressure measures force per unit area, with S.I unit of pascals (1N/m²).on average, a column of air with a cross-sectional area of 1cm²,measured from mean (average) sea level to the top of earth's atmosphere, has a mass of about 1.03 kg and exerts a force or weight of about 10.1 newtons, resulting in a pressure at sea level of about 10.1 N/m² or 101 KN/m².