1. The board is equipped with built-in charging management and charging and discharging protection2. The calibration value is a six and a half digit count, accurate and reliable. According to usage requirements, it is recommended to recalibrate the calibration conditions every two years. The time and calibration value record card will be pasted on the benchmark3. With indicator lights, press and hold for 2 seconds before turning on. When turning on, all four indicator lights simultaneously4. This product is a precision voltage reference that can be programmed with four common output voltages: 10.0 V, 7.50 V, 5.00 V, and 2.50 V5. Voltage output interface with 2mm copper test socket for easy insertion into a pen type multimeter for measuring or calibrating other instruments. Charging and discharging interface:micro-USB. Output interface:2mm banana socketBattery:300mAH benchmark dedicated battery (product does not include batteries)Battery voltage:3.7VBattery model:14250Voltage:DC 5VInstructions:1. The benchmark is not used to fully charge the battery every two months. The board is equipped with built-in charging management and charging and discharging protection. Please note that the battery polarity should not be reversed2. The output interface is a 2mm banana socket, and there is also an SMA output interface calibration. The HP3458A eight and a half digit multimeter is used for calibration (after sufficient preheating), and the calibration value is six and a half digits for counting, which is accurate and reliable. According to usage requirements, it is recommended to recalibrate the calibration conditions every two years. The time and calibration value record card will be pasted on the benchmark, please keep it properly3. Press and hold for 2 seconds before turning on the machine.When turning on, all four indicator lights will at the same time, and then output a 2.5V reference voltage. After turning on the machine, briefly press the button to switch gears, in order of 2.5V-5V-7.5V-10V. Press and hold for 3 seconds to turn off the machine. After turning off the machine, the voltage indicator light will immediately turn offColour:YellowMaterial:PC+MetalPackage Contents:1 x voltage reference boardOnly the above package content, other products are not included.Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.