Gauge Sensors are sensors that show pressures above atmospheric pressure -- when exposed to the atmosphere they will report a reading of zero pressure. Gauge sensors are designated by a 'g' or the word 'gauge' at the end of the rated pressure reading range.
Absolute Sensors are sensors that show the pressure based on an absolute scale starting with zero being a perfect vacuum. These sensor exposed to the atmosphere will show approximately 1 bar (1.013 at sea level), or lower at higher elevations. Abosolute sensors are designated by an 'a' or the word 'absolute' at the end of the rated pressure reading range.
Typical uses: Oil pressure, fuel pressore, map sensor, brake pressure sensor, clutch pressure sensor, cooling system pressure, etc.