Most people are typically accustomed to dealing in gage pressure, that is, pressure relative to the normal atmospheric pressure which surrounds us. As such. “absolute” pressure and absolute pressure sensor which measure pressure relative to a perfect can be somewhat confusing.  Also, because zero absolute pressure (a perfect vacuum) is impossible to achieve, it is much harder to measure and calibrate absolute pressure sensors. This application will discuss what absolute pressure is, how it is best measured and how to calibrate absolute pressure sensors.