Atmospheric pressure gauge in physics, the latitude of 45 degrees of sea level ( The first is zero) The perennial average atmospheric pressure regulation for standard atmospheric pressure (1 atm) 。 This standard atmospheric pressure to a certain value. Its value is 1 standard atmospheric pressure = 760 mm hg = 1. Project 033 atmospheres = 1. 5 of 0133 X 10 square handkerchief = 0. 10133 mpa atmospheric pressure is the result of the earth's gravitational pull, due to the earth's gravity, air is sucked into the earth, creating a pressure, zui stressful atmosphere near the ground. Pressure on climate science, it is to point to the weight of per unit area is big column ( Atmospheric pressure) , that is, large gas column pressure on unit area. Air pressure units are mm and millibars two kinds: with the height of mercury column to represent the air pressure unit, with the mm ( 毫米) 。 Such as air pressure is 760 mm, it is said at the time of the atmospheric pressure and the pressure produced by 760 mm high mercury is equal. Another kind is the radio weather forecast often hear millibars ( mb) 。 Atmospheric pressure gauge is used by large gas column pressure on unit area the size of the air pressure of the unit. 1 = 1000 dyne per square centimeter ( One bar = 1000 millibars) 。 So 1 millibars said on l square centimeters area by l000 dyne acting force. When air pressure is 760 mm is equivalent to 1013. 25 millibars, the pressure value is called a standard atmospheric pressure. Is changing with height and air pressure. The higher the altitude, the smaller the atmospheric pressure; The cities of the elevation difference between the disparity, the pressure difference also. Big column is affected by the density change, the weight of the atmospheric pressure air density is larger, also is the more per unit volume of air quality, produced by the atmospheric pressure is the greater. Atmospheric pressure is measured on the surface of the earth covered with a thick layer of the atmosphere of air. The objects in the atmosphere, to be by the pressure of the collision of the air molecules, the pressure is called the atmospheric pressure. Also can be thought of, the atmospheric pressure is objects in the atmosphere by the atmosphere of its own gravity pressure acting on the object. Due to the gravity effect, from the surface of the earth, the earth's attraction is big, the molecules of air intensity is high, the impact to the high frequency on the surface of the object, the resulting atmospheric pressure is big. Atmospheric pressure gauge away from the surface of the earth, the earth less attractive, the molecules of air intensity is low, the impact to the surface of the object frequency is low, the resulting atmospheric pressure was low. So in different height of the atmospheric pressure on the earth is different, the smaller the higher the atmospheric pressure. In addition, the temperature and the humidity of the air of atmospheric pressure may also be affected.