DGC DC-3000 Series Instruction Manual page 19

DC-3000 SERIES ULTRASONIC THICKNESS GAUGE
②If there are large quantity coupling agents attached on the measured
surface, when taking away the probe, it will cause error. so when the
measurement is completed, please move the probe away from the
measured surface quickly.
③If the probe wears out, it will cause the displayed value unstable, please
replace the probe.
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