The BAPI AQX Quantum Series CO2 Sensor is an accurate and reliable way of incorporating demand controlled ventilation into a building's HVAC strategy. It measures the CO2 in ranges of 0 to 2,000, 0 to 5,000, 0 to 10,000 and 0 to 50,000 ppm with a field selectable output of 0 to 5 or 0 to 10 VDC. The Single Channel unit has been optimized for periodically unoccupied areas and features automatic background calibration over a long time period to reduce drift. The Dual Channel 24/7 unit has been optimized for continuously occupied areas and features a three-point calibration process for enhanced stability, accuracy and reliability. Air pressure changes from altitude or weather patterns can affect the output of CO2 sensors, even putting them outside of their specified accuracy. The BAPI unit has a built-in barometric sensor that continuously compensates the output for accurate readings despite the weather or altitude of the installation. For 0 to 2000 PPM units, the CO2 level is indicated as in.Good, Fair or Poor in. by three discrete green, yellow and red LED's on the front of the unit. If it reaches the top of the PPM range, the red LED will begin to flash.