The Air Breather Check (ABC) takes the guesswork out of when to change your air breather because it doesn't care how dirty the air breather looks or how long it's been installed. It only cares how well the breather is working. The air breather check is calibrated in inches of water and will activate, providing a visual indication, when a vacuum equivalent of 15 inches of water (3.75 kPa) is reached. The ABC can be reset simply by depressing the yellow button and used over and over again.