Absolute (PSIa) Pressure Sensors
AEM high-quality stainless steel PSIa sensor 50 (3.5BAR) PSIa is referenced to absolute zero. Absolute zero is the pressure measurement when all the pressure exerted by the atmosphere has been removed. The most common use for absolute pressure sensors is reading manifold pressure. PSIa sensors are required if you wish to measure a vacuum. A PSIa sensor will read about 14.7 PSI when the sensing element is exposed to atmospheric pressure at sea level however they can be recalibrated to read zero at atmospheric and a negative number at values less than atmospheric pressure.

Stainless Pressure Sensor
Use a SS Pressure Sensor where you need exact details of the pressure.
Example: MAP Sensor information for the ECU Calibration/crucial information for the ECU.