Planck's constant is determined using the photoelectric effect with a photoelectric tube. The red lamp lights up when the power is turned on, but the usage and complete functionality are unknown. When the power is turned on, a maximum DC voltage of -1.99V is generated at the output of the IP-39 photoelectric tube, and it changes with the dial. There is a viewing window-like structure on the right side, but there are no attachments. Please consider the item as is. Shipping size: 60.