[quote name=\'clemon79\' post=\'118980\' date=\'May 20 2006, 01:05 PM\']
This is just a guess.
It strikes me that it's a technology kinda like light diffusion, in that there are ten slabs of glass in there, one with each number on it, and then each one has a bulb at the BOTTOM of it, and when the appropriate bulb is turned on, the light shines through the edge of that bit of glass only, which makes that number visible. Kinda like the technology that make your GameBoy work.
(That said, I don't know if that technology was refined enough to use in that application back then, but it makes more sense to me than the slide theory.)
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Your description sorta makes me want to call it 1st generation fiber-optics. I also know that Otis Elevators used that J! technology in the 70's in some of their floor indicator displays. And it was indeed a different light for each number.