ISO 2808-7B, BS 3900-C5 method 7B, ASTM D4414-A specify that the wet film wheel should be perpendicular to the substrate and the thickness of the coating should be stated as that indicated on the central wheel - ensuring that the wheel has been rolled from maximum thickness to minimum thickness - thus avoiding surface tension.

Example

Hold the wheel by its central spindle. Begin at maximum thickness to reduce risk of inaccuracy caused by surface tension.

Roll the wheel through the wet film with the side 1 in the diagram touching the substrate. Roll for at least one whole turn and slowly enough for wetting to occur. Roll the wheel backwards by at least on complete turn. The wet film thickness is read from the scale, at the end of the wetted segment of the middle circle, 2 in the diagram

To use wheel on pipes, measure across the longitudinal axis （lengthways） of the pipe.

On rough surfaces, measurements will be made from the surface peaks and represent the minimum wet film thickness.

Elcometer 3230 濕膜輪