The CO2 sensor in the ML206 Gas Analyzer will output either "Out of Range" or 0% CO2 for the first 2-5 minutes of operation. After this period of time, the sensor will begin to output CO2 % values. ADInstruments recommends allowing the ML206 Gas Analyzer to warm up for at least 10 minutes with the pump on prior to use (see page 20 in the Gas Analyzer Owner's Guide). Until the Gas Analyzer has warmed up fully, the output from the CO2 sensor may be unusable due to a large offset and/or thermal drift.