Feature: 1. Reference Module: Programmable 4 channel voltage calibration module, with built in charging management, loading and unloading protection, ensuring safe and reliable operation. 2. Multimeter Calibration: Use for HP3458A 8 and a half digit multimeter for calibration (use after sufficient preheating), with a calibration value of 6 and a half digit counting, accurate and reliable. 3. With Indicator Light: The voltage calibration board is equipped with indicator light. Press and hold for 2 seconds before turning on. After turning on, all 4 indicators will light up simultaneously. 4. Output Voltage Setting: With precise reference voltage source, this module can set 4 commonly used output voltages, namely 10.0V, 7.50V, 5.00V, and 2.50V, with a wide range of applications. 5. Micro USB Interface: This module has Micro USB charging and discharging interface, with 2mm copper test socket, easy to insert into a multimeter to measure or calibrate other instruments. Specification: Item Type: Reference Voltage Board Material: PCB Battery: 1 x 3.7V 14250 Battery (battery not included) Battery: Benchmark Special Battery Charging and Discharging Interface: Micro USB Voltage: DC5V Output Interface: 2mm Banana Socket. Package List: 1 x Reference Voltage Module Note: The reference voltage does not need to be fully charged every 2 months. The board has built in charging management and discharge protection. Do not reverse the polarity of the battery.