The Thin Film Gauge consists of a flat, circular 1/16" thick stainless steel disc with forty machined notches around the periphery and below the rim surface.
Roll the gauge across the surface in a perpendicular position to wet the numbered flat surfaces below the surface of the paint film. After rolling the gauge (or slightly rocking it when areas are small) inspect the notched faces. The wet film thickness lies between the highest not-wetted and wetted faces.
When measurements are made on a clear coating, after rotation of the gauge over the wet film, dust talcum powder on the flat faces and then blow it off. Talc will adhere only to the wetted faces.