Input Voltage Range: 4-40VDC Output Voltage Range: 1.25-37DC Adjustable Output Current: 2A Voltmeter Range: 0 to 40V, +-0.1V ErrorReverse Polarity Protection InputBuilt-in Short Output Protection FunctionBuilt-in Thermal Shutdown FunctionL x W x H=6.1x3.4x12cm (Approx)LED Digital Voltmeter Tube, Accuracy is Adjustable Function, Can Be Directed At Your Multimeter Adjustable AccuratePress Right Key To Make The Display Show Voltage input or output. When the right led light "OUT" shows the output, the left led input "in" shows Quantity: 1PCow to adjust the accuracy? Output Voltage Calibration StepsStep 1, set the right button to "OUT" with LED backlight, the voltmeter shows the output voltage value; Press the right button for more than 2 seconds, release, the voltmeter and the "OUT" LED flash in synchronization, so you can enter the output voltage calibration mode. Step 2, press the right button (normal speed), the voltage value sums up the unit; Press the left button, minus the unit; Due to the unit is less than 0.1V, the minimum voltage indicator is 0.1V, so you need to keep pressing 1-5 times to see the voltmeter change 0.1V, How many times the voltmeter changes 0.1V by pressing the key, depending on the current display voltage, the higher the voltage, the lower the number of presses. Step 3, press the right button for more than 2 seconds, release to exit the output voltage calibration mode. All parameters set to auto shut off to save. Input Voltage Calibration StepsStep 1, set the right button to "IN" with LED backlight, the voltmeter shows the input voltage value; Press the right button for more than 2 seconds, release, the voltmeter and the "IN" LED flash in synchronization, so you can enter the input voltage calibration mode. Steps 2 and 3, according to the output voltage calibration method. NoteSome customers report: "the module cannot be adjusted, the output voltage is always equal to the input voltage." When you encounter this problem, turn the potentiometer counterclockwise 10 laps or more, and then adjust the output voltage. Because the factory default output voltage is 20V. Package Included:1 x LM2596 DC 4.0 - 40 to 1.3-37V LED Voltmeter Buck Step-down Power Converter Module