Seven segment display history

While definitely newer than the 1910 patent mentioned earlier, I have a mechanical 7 segment clock. I think it was made somewhere in the late 70's/early 80's (woodgrain plastic). From the front, it resembles a run of the mill digital clock, save for the fact that the display is white-orange. Inside is a purely mechanical contrivance with plastic cards with slots cut in them. A light bulb shines through them and "projects" the numbers onto the face. It's really cool, if only for the fact that it's unusual. Not only can you hear the motor changing the numbers, but when the numbers change, they kinda "melt" into one another, as segments don't instantly flick off all at once. It was made by General Electric. My assumption was that they wanted to get the style of the then-expensive digital LED clock, but make it cheap. (motors and mechanical stuff used to actually be cheaper than electronics - remember that?). -Ian