The Filter Minder® filter monitoring device makes it easy for you to tell when it's time to change filters. 
Air filter restriction is 
The Filter Minder® can be found on a wide variety of
The Filter Minder® reads the restriction in the air induction system. Air filters usually have low restriction for most of their service life, and the position indicator will not move very much. Then, as the air filter reaches the end of available service life, filter restriction increases rapidly, and the position indicator of the service indicator will move faster towards the red zone.
The chart below illustrates typical air filter restriction readings. Click to enlarge.
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Air filter restriction usually remains low through most of the filter service life, then increases rapidly at the end.
