Digital Sundial Ubercool.

[Tuckerfan]

So much for thinking that they were ancient technology. Lest you think that I’m pulling your leg, gaze upon this image:

Yeah, that’s it working.

Here’s a simplified explaination of the prinicples behind it.

The sundial consists of two closely spaced parallel masks. The first mask, facing the sun, has a regular array of thin vertical slits, which cast a striped light pattern onto the second mask. That mask, facing the visitor, is composed of narrow stripes, cut from the digits to be displayed. These stripes are intermingled, so that they are illuminated consecutively. The figures below illustrate this in a simplified example for the right-most numeral, which is either a “0” or a “5”.

As the site goes on to make clear, it’s a little more complicated than that, but not too much.