A Primer on Vacuum Pressure Measurement

It's often said that we live at the bottom of a sea of air. Looking more closely at the atmosphere around us it is composed of a variety of molecules such as nitrogen, oxygen, water vapor, carbon dioxide, argon and a host of other natural and manmade substances. The density of this mixture of molecules is determined by such factors as the total depth of the atmosphere, ambient temperature, altitude and meteorological conditions. At the microscopic level, the molecules are in motion and the combined force exerted by this vibrating mass of molecules on a surface is something we call pressure.