This is a unique clock that uses a Russian Numatron tube. The tube is a seven segment display that uses incandescent filaments for each of the segments. This technology is from the same period that the now popular Nixie tubes, however it operates at low voltage and glows with a yellow color. The kit contains incandescent Edison base tube as the display case for this single digit clock, It is a bulb within a bulb. A single digit clock flashes out the time one digit at a time. There are four bulbs that indicate which digit is currently displayed (Tens of Hours, Hours, Tens of Minutes and Minutes).