This instrument is similar to the Elcometer 3230 Wet Film Wheel, but is designed for use in the coil coating process.
The outer wheels are knurled to allow measurements to be taken on slippery coatings or on fast moving substrates.
By rolling the gauge through a wet coating, the centre wheel eventually touches the film. This point on the scale indicates the thickness.
When the volume to solids ratio of the coating is known (generally found on the product data sheet supplied by the manufacturer), the wet film thickness can be used to predict the dry film thickness.