Extech CO250 Portable Indoor Air Quality CO2 Meter/Datalogger Measures Carbon Dioxide (CO2), temperature, humidity, dew point, and wet bulb Checks for Carbon Dioxide (CO2) concentrations Calculates statistical weighted averages of TWA (8 hour time weighted average) and STEL (15 minute short term exposure limit) Maintenance free NDIR (non-dispersive infrared) CO2 sensor CO2 measurement range: 0 to 5,000 ppm;