The Extech CO220 air quality CO2 sensor monitors carbon dioxide, temperature, and humidity. The CO220 also determines the dew point and wet bulb. Use in conference rooms, schools, greenhouses, factories, hotels, hospitals, and other areas where significant volumes of carbon dioxide are produced. It computes statistical weighted averages for TWA (8-hour Time Weighted Average) and STEL (15-minute Short Term Exposure Limit). Maintenance-free NDIR (non-dispersive infrared) CO2 sensor. It can manually save and recall 99 readings. Complete with an AC adapter.