Absolute (PSIa) Brass Pressure Sensors AEM offer high quality brass PSIa sensors in 30(2BAR), 50 (3.5BAR) and 75 (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 of you wish to measure 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. Which Pressure Sensor is right for you? There are many different tools that can be used for measurement, but the degree of accuracy is dependent upon the tool. For example, a ruler can measure distance with a good degree of accuracy, but for a more precise measurement a caliper should be used. The difference between a brass pressure sensor and a stainless steel pressure sensor is similar if we think about it in these terms: Brass Pressure Sensor = Ruler Use a Brass Pressure Sensor where you need a good reference to what pressure is being seen. Example: Brass Pressure Sensor used for a Boost Gauge - Reference/Information for knowing manifold pressure, not for ECU calibration. Stainless Pressure Sensor = Caliper 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.