Features: Specially voltage reference module, it use low-temperature drift components, Type C 5V port as power supply, use filter to make the power supply purer and smoother, no need battery to supply power. Used to verifies the accuracy and linear of handheld 3 1/2 digital multimeters. Used to verifies the accuracy and linear of handheld 4 1/2 digital multimeters, must keep the same temperature and humidity as the data sheet specified. The pull switches can only keep one ON each time, no two ON allowed at the same working time. If you like to verifies the accuracy and linear of handheld 4 1/2 digital multimeters, try to keep the same temperature and humidity as the data sheet specified. Try to verifies in a low air flows environment, try to avoid direct cold wind from the air conditioner as it may cause some additional errors. Specifications: Size:Approx.8.5x5.50cm/3.35x2.17inch Package Includes: 1Pc Voltage Reference Module note: 1.Please allow 1-2cm errors due to manual measurement, making sure that you not mind before order. 2.Due to the differences between different monitors, the picture may not reflect the actual of the item.