Estone Digital Ultrasonic Thickness Meter Tester Gauge Metal Tester 1.2-220mm GM100 Measuring Sound Velocity with a given thickness When the given thickness is over 20mm, the accuracy is +/- 1%; when the given thickness is less than 20mm, the accuracy is +/- 5% Measurement Range: 1.2-225.0mm (Steel) Each package with a cell phone chain Which has "Estone" LOGO