The Triplett Model GSM450 Carbon Monoxide/Carbon Dioxide IAQ Datalogger Meter measures CO, CO2, Temperature, Humidity, Wet Bulb and Dew Point and can be used to measure air quality in office buildings, schools, exhibition halls, shopping malls, meeting rooms, fitness centers, restaurants and other public places. Manually step through CO, CO2, Temperature, Humidity, Wet Bulb and Dew Point to display each reading on its large backlit LCD display. It features TWA (Time Weighted Average - 8 hours) and STEL (Short Term Exposure Limit - 15 minute weighted average) measurement with a user-adjustable 80dB CO alarm level. You can manually store/recall up to 99 readings and datalog up to 32,000 readings. Additional features include real time clock, Min/Max to record the highest and lowest readings, Data Hold freezes the reading on the display, and Auto power off with disable to conserve battery life. °F/°C selectable. Includes (4) AA batteries, mini USB cable, and carrying case.