The CarbonMatic is a CO2 controller with double functionality. The controller may, based on the value CO2 in a room activate an extractor fan when the CO2 level is higher than the set value. In addition, the CO2 controller may activate the valves of a CO2 booster to add CO2 into the room when the level is below the set value. The light sensor makes sure that the CarbonMatic, in CO2 + mode, activates only in daytime. The CarbonMatic displays the measured room CO2 value in ppm, divided by 100.