To make sure you understand, it doesn't measure airflow, just sealed suction. Humans can pull more sealed suction on this guage with their mouth then any vacuum could but we don't make good vacuums because we don't have the ability to inhale tons of air. These also will not tell you if you have a clog. Even with a clog, the sealed measurement will be the same though in may take a little more time to build up the suction. It will tell you if there is a hole in your system because the suction will be a lot less than is rated for the motor.