TNB NATURALS - CO2 MONITORTNB Naturals CO2 Monitor and Thermo Hygrometer is a sleek portable unit that has been developed to monitor and display CO2 concentration, ambient temperature and relative humidity, along with the year, month, date and time. The monitor has a 3. 5' LCD display and is USB compatible with a logging memory of 12,700 units. It has an accuracy of + or 50 PPM and has the capability to read CO2 levels as high as 9999 PPM. The unit features a built in warning