This is like a thermostat for your CO2. Of course it is not a thermostat but it is as simple to use as that. Just set your desired CO2 level and there you have it. It's just that easy. The SPC-2 monitor uses infrared technology to turn CO2 equipment on and off based on a 20 ppm variable and not allow it to operate at night. In this diagram it is plugged into a CT-DH-3 atmospheric controller to coordinate with ventilation but you could just as well use it without the CT-DH-3 as a stand alone CO2 controller.