The Reed R7920 is a compact ultrasonic thickness gauge covering 0.04-11.8 in (1-300mm) with a 2.4 in backlit monochrome display and a rechargeable lithium battery good for about 16 hours of use. It's built to check steel, cast iron, aluminum, brass, zinc, various plastics and other common shop materials, storing up to 300 readings in memory with adjustable high/low alarms and automatic material calibration.