The Extech CO250 Portable Indoor Air Quality CO2 Meter measures Carbon Dioxide (C02), Temperature, Humidity, Dew Point, and Wet Bulb. Checks for Carbon Dioxide (CO2) concentrations and calculates statistical weighted averages of TWA (8 hour time weighted average) and STEL (15 minute short term exposure limit). User programmable audible alarm. Data acquisition software and cable included to record and document CO2, Humidity and Temperature data.