The PGI is the right choice for the visual flatness check of polished surfaces. For testing, the parts are simply placed onto the glass surface on the top side of the PGI. A magnified image of the part and the fringes is displayed on a monitor and can be gauged thus reliably. A fast documentation of the flatness is possible with our software INTDOK or an optional video printer. The interpretation of the fringes is alike as with an optical flat: straight, parallel and evenly spaced fringes indicate a high degree of flatness. Data subject to modifications. July 2013