Wet film wheels are high precision, accurate and easy to use instruments consisting of a set of three wheels, with measurement ranges from 0-25μm to 0-3000μm.
Using a wet film wheel: roll the wheel 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 a product data sheet, the wet film thickness can be used to predict the dry film thickness. Roll from maximum to minimum to avoid a false reading caused by surface tension.
For more information, see the Elcometer Guide to Wet Film Thickness.