Features: The K4212H579 programmable 4 channel voltages calibration module integrates charging management and load/unloads functions, delivering six digit precisions for HP3458A multimeter calibration with built in reference voltages source. Featuring four preset outputs (10V/7.5V/5V/2.5V), double color LED indicators, and USB port with 2mm copper test sockets for seamless connectivity to measurement instruments. Designed for electronics engineers and calibration technicians requiring high accuracy voltages references in laboratory environments or precisions equipment maintenance scenarios. Ideal for verifying multimeter accuracy in labs, manufacturing quality controls stations, or field service operations where stable voltages benchmarks are critical. Its compact PCB design with instantly start functionality (hold power button for 2s) ensures rapid deployment across diverse calibration workflows while maintaining measurement consistency. Specifications: Component: PCB Battery: 1piece 3.7V 14250 Battery (battery not included) Charging and Discharge Interfaces: USB voltages: DC5V Output interfaces: 2mm banana plug Notes:The reference voltages does not need to be filled every 2 months. The development board has built-in charging management and discharge functions. Do not connection the battery polarity reversely. Package Includes: 1Piece voltages Reference Module note: Please allow 1mm errors due to manual measurement. Due to the differences between different monitors, the picture may not reflect the actual color of the item.