1. Long Press the Button for more than 4 Seconds, then Release, Voltmeter and IN Led Flash in Synchronization Entering into the Input Voltage Calibration Mode. 2. Press the Button in a Short Time (1 Second) to Adjust the Value (range from -0.5 – 0.5V), Positive means to Rises Units, Negative means to Minus Units. (Due to a unit is less than 0.1V, so you have to Continuously Press 1 to 5 times to see the Voltmeter change 0.1V). 3. Long Press the Button for more than 2 Seconds and then Release to Enter the Output Voltage Calibration Mode. 4. After Calibration, Long Press the Button for more than 2 Seconds all Parameters will be saved Automatically and Back to the Voltage Display. How to use: 1. Press the button in a short time (1 second) so that “in” LED lighted, the voltmeter shows the value of input voltage. 2. Press the button in a short time (1 second) again so that “out” LED lighted, the voltmeter shows the value of output voltage. 3. Rotate the top screw of potentiometer clockwise to boost the value of the output voltage, anti-clockwise to reduce it. 4. Long press the button between 1 and 4 seconds to turn off the voltmeter. How to adjust accuracy of input/output voltage: (for the person who need a highly accurate value of number) 1. Long press the button for more than 4 seconds, then release, voltmeter and “in” LED flash in synchronization entering into the input voltage calibration mode. 2. Press the button in a short time (1 second) to adjust the value (range from -0.5 – 0.5V), positive means to rises units, negative means to minus units. (Due to a unit is less than 0.1V, so you have to continuously press 1 to 5 times to see the voltmeter change 0.1V). 3. Long press the button for more than 2 seconds and then release to enter the output voltage calibration mode. 4. After calibration, long press the button for more than 2 seconds all parameters will be saved automatically and back to the voltage display.