DROK High Accuracy 20V DC Digital Voltmeter +/- 0-19.999V 5 Digits Red LED Voltage Tester 0.001V Resolution for Positive Negative Volts Measurement with Polarity Protection +/-19.999V full measure range, it will show "H" if over- range. It can measure positive and negative DC +5V +/-5% operating power supply with low current consumption. 0.56" red LED digital tube with bright clear voltage high accuracy reading. Selectable decimal point position, with calibration potentiometer. With polarity protection circuit, it will not be burnt if the power supply positive and negative are