Some of the more sophisticated models offer a memory function and can store data from multiple tests for later retrieval and analysis. A few can dump their stored data into computers for archival storage, in case you need to analyze data that spans multiple jobs over a period of time. Another benefit of testing the film thickness is preventing you from throwing away expensive coatings. If you apply 30 mils of wet coating thickness because you're trying to achieve a 20-mil dry coating thickness, you may be applying too much product. The distance at which the magnet releases from the substrate is converted into the coating's thickness, usually by markings on the device.
Destructive tests are another option.
A Tooke gauge is a common destructive-testing device that slices through the dry film to measure thickness. The thickness of different coats can be measured individually, if they are different colors. Destructive testing is particularly important for contractors who are repainting structures, Beamish said. It doesn't hurt to make a few notches in the existing paint. It not only will tell you how thick the entire coating is, it also will tell you how thick individual coats are.