This is a DC-DC Step Down Power Supply Adjustable Module With LCD Display, the display using STN liquid crystal display screen, voltage and current can be displayed simultaneously, blue background and white character, wide angle and wide field of view. It start used button to adjust voltage, left button to reduced the voltage, the right button to increasing voltage, press button once can adjust 0.04V voltage, if you hold more than 1s, you can quickly adjust voltage. Calibration method: Under power off situation, Holdind left button and power the supply,when the  display begin flashing, release left button, with multimeter measuring the output voltage, by press the left and right button ,adjust the multimeter measuring voltage near 5V, such as 5.00V ,4.98V or 5.02V is ok too,at this situation,please ignore the displaying on this item. After adjustment,please power off it and then power to it again, then the  calibration is completed. Errors can be calibrated in 0.04V, if the error is greater, you can try to calibrate it again.