Definition

• The definition of absolute pressure is the pressure of having no matter inside a space, or a perfect vacuum. Measurements taken in absolute pressure use this absolute zero as their reference point. The definition of sealed-gauge pressure is the pressure measured through a sealed device in which the zero point is set. This set point is whatever the pressure inside of the device was before sealing, which the manufacturer of the sealed pressure gauge decides.
  
  

Units

• To denote absolute pressure, you put a capital A after your units of pressure, such as 0PSIA or 9mmHgA. To denote sealed gauge pressure you write an SG or an S after your pressure, such as 17PSISG or 29mmHgS.
  
  

Applications

• Depending on why you are measuring pressure, you will find it more useful to use either absolute pressure or sealed gauge pressure. Absolute pressure is the measure for barometric readings such as those used for weather patterns, while sealed gauge pressure is useful for high-pressure applications such as hydraulics.
  
  

Manufacture of the Sensors

• Absolute pressure sensors and sealed gauge pressure sensors have very different manufacture specifications, as the two types of pressure readings are useful for very different applications. For example, the base construction of the sensing element is fundamentally different, as different materials can sense the high pressures of sealed gauge pressure and the low pressures of absolute pressure with varying accuracy.