WETG : Wet Thickness Gauge

Wet thickness testing is required on fluid and liquid applied membranes.
Wet thickness can be measured by a comb gauge, the most commonly used field gauge.
A comb gauge has calibrated notches on its edges. You place the gauge squarely into the film and on the substrate when the coating is wet.
When you remove the gauge, look at the notches. The film's thickness lies halfway between the last coated notch and the adjacent uncoated notch.