Ultrasonic Thickness Gages measure the thickness of a part by measuring the time sound travels from the transducer through the material to the back end of a part, and then measures the time of reflection back to the transducer. The gage then calculates the thickness based on the velocity of sound through the material being tested. Calibration of the Ultrasonic Thickness Gauge is simple and done with a sample of the material to be measured (of a known thickness), or the sound velocity specification of the material (depending on model). Parallel surfaces are a must for this type of tester! There are several models available; some are able to measure down to .010" and up to 20" thick. All models are on sale. Measure Smarter with Gaging.com!