DROK Waterproof Digital DC Voltmeter 3.3-30V Voltage Tester Meter Gauge Volt Meter with Two Wires and 0.52" Green LED Display for Electro car Motorcycle Small Voltage Meter: Waterproof voltmeter or voltage detector with 0.52 inch. Potentiometer: Built in trimmer potentiometer, it is simple to do a calibration work. Reverse Connection Protection: Reverse connection protection, No worry it will burn your meter when get it connected reversely. Easy and Convenient Installation: two wires, just connect the red wire to the positive and connect the black wire to the negative. Wide Application: suitable for most of electrical Bike, motor and etc, will be a good tool to detect Voltage.