Wet film thickness can be measured in a variety of ways. To measure the amount of oil in our cars we use a dipstick. Using an adaptation of this simple technique, the coatings industry use combs and wheels to accurately measure the wet film thickness.
The wet film thickness of most organic coatings including paints, resins, lacquers, varnishes, gel coat etc may be measured before curing. It gives the inspector a quick, low cost method of checking the thickness of freshly applied coatings.