eCO2 – means estimated concentration of carbon dioxide calculated from known TVOC concentration. This is based on the assumption that the VOC produced by humans is proportional to their exhaled CO2. That means it gives similar signal to real CO2 sensor, in the case the main, prevailing source of air pollution in such room are people who stay inside. The analogue output of the VOC sensor is in the range 400 – 2000 ppm eCO2.