CO2 Monitor Controller Model # 2002A and 2002B by Control Wizard Products. These two units work together to give outstanding results and value to the customer. They can be purchased seperately, see product number CO 350 and CO 351.This combo has been designed to turn CO2 equipment ON and OFF at preset levels by reading the Monitors signal output. Simply plug in your CO2 equipment in the outlet provided. Then, plug one of its power cords into a wall outlet and the other cord into a controlled power outlet (like you would find on any brand of atmospheric controller or timer) that powers your exhaust fans. When the exhaust fans are powered the Controller will automatically turn your CO2 equipment OFF. This saves CO2 from being vented while the area is being cooled. When the exhaust fans shut OFF the CO2 equipment is allowed to fill the room to your pre-set levels. The Monitor reads from 0-5000 PPM CO2. Preset levels are adjusted within the monitor. The comfort or working zone is 300 PPM. 150 PPM below and 150 PPM above your preset level. 1500 PPM is generally regarded to be the optimum preset level.