Restriction Gauges, also known as filter minders are great air filter service indicators. The restriction gauge/Filter Minder is installed on the air cleaner or air induction piping so that it has access to clean filtered air (between air filter and engine). The air filter restriction gauge service indicator is a simple device that accurately measures and remembers the highest restriction at maximum air flow. The air restriction indicator is easy to read. As the air filter plugs, and restriction increases, the yellow position indicator moves in the clear window and locks at several points. When it reaches and locks in the red zone, the air filter should be changed and the indicator reset to zero. Reset the indicator by pushing the yellow reset at the end of the indicator.