Simple to install air filter gage for media style air cleaners. This simple device is mounted on the face of your furnace or air handler blower door using the included double stick tape. All you need to do is drill a 3/8 hole in the door and push the attached probe into the hole. Now install a new filter media, turn on your furnace fan and adjust the calibration screw so the indicator needle is in between the green bars. As your filter media clogs, the needle will move into the red zone. Installs in just minutes and lasts for years. Calibration is only required once. Can be remotely mounted up to 10 feet using optional G9914 kit available here.