Analog Control: using a mini screwdriver to increase or decrease output voltage by adjusting the screw, clockwise to step up voltage and counterclockwise to step down voltage. Has very stable output, input range is DC 4~40V and output range is DC 1.25~37V, please make sure the input voltage should be higher than output voltage at least 1V. Can be used for many electronic projects. Press the button next to voltmeter to test input voltage or output voltage. Green LED lights on when testing output voltage; red LED lights on when testing input voltage. With input and output voltage measurement error calibration function; Wiring terminals require no soldering iron and create convenient usage. Press the button for 1 to 4 seconds, voltmeter would be shut off when releasing your hands; the voltmeter is very accurate.