CO2 METER, + Humidity, Temperature. 
GCH-2018 
* CO2 range : 0 to 4,000 ppm. 
* CO2 sensor : NDIR, long term reliability. 
* CO2 with alarm setting. 
* Function : CO2 (Carbon dioxide), Humidity, Dew point, Temperature.
* Data hold, Record (Max., Min.). 
* RS232/USB computer interface.