Product Description: - 3 Independent CO2, humidity and temperature sensors. - User operated CO2 calibration. - USB datalogg: 50,000 records. - Internal backup battery to maintain date/time setting. - Power management IC to increase batter efficiency. - Easy- to-Use PC software for parameter settings and data analysis. - Internal CO2 alarm buzzer. Application:  ST-501 is an excellent indoor air quality (IAQ) instrument measuring the carbon dioxide (CO2), Relative Humidity (RH) and Temperature.  - Building HVAC monitoring.  - Indoor air quality survey.  - Locate the presence of combustion fumes from vehicles and appliances.  Specification:  - CO2 Sensing Method: NDIR (Non-Dispersive Infrared)  - Measures: Carbon dioxide in PPM, temperature (F or C), % Relative Humidity  - CO2 Measurement range: 0~9999 ppm (2001~9999 ppm over range)  - CO2 Accuracy: 75ppm, 8% of reading (0~2000 ppm)  - Display Resolution - 1 ppm  - Datalogging: 50,000 records, - Fast USB download (50,000 records in less than 10 seconds.)           CO2 Sensor           Type     Non-dispersive infra-red (NDIR)           Measurement Range     0~9999 ppm (2001~9999 ppm over range)           Accuracy     75ppm, 8% of reading (0~2000 ppm)           Resolution     1 ppm           Response Time     2 seconds                      Relative Humidity Sensor     Temperature Sensor:           Type     CMOSens     Type     Thermistor           Measurement Range     1% ~99%     Measurement Range     0 to 50C           Accuracy     3.0%RH(20~80%) 5.0%RH(80%)     Accuracy     0.5C from 0-50C           Resolution     0.1%     Resolution     0.1C           Response Time     8 Seconds     Response Time     1 seconds