These instructions explain how to install a Filter Minder ® Grommet Mounted Air Filter Monitor in your automobile. Begin >> Begin >> Engineered Products Co. 2940 Airport Blvd. Waterloo, IA 50703 Ph: (319) 234-0231 Fax: (319) 234-8922 info@filterminder.com  Normal clean filter Used filter with some restriction Used filter with maximum recommended restriction. Filter should be changed.