The Reed R7900 is a handheld ultrasonic thickness gauge that reads material thickness from a single side, covering 0.03-15.7 in (0.65-400mm) with accuracy down to +/-0.04mm on thinner sections. Its backlit 4-digit LCD shows sound velocity on demand, and onboard memory logs up to 500 readings across five files. It works across metals, plastics, ceramics, composites, epoxies and glass, with adjustable high/low alarms and a built-in two-point calibration routine, running roughly 100 hours on two AA batteries.