In the days before digital number readouts (we're talking 1950s and '60s) electronic devices that needed to display changing numbers used nixie tubes, which were little cathode tubes filled with a stack of individual, tiny neon lights shaped like the numbers 0 through 9. Evil Mad Scientist Laboratories got their hands on one of these and ripped it open to show you the cool guts.
The limitations of the technology are obvious--numbers further back in the stack appeared fainter than those up front, and the skinny "1" is double-tubed to produce the illumination required for legibility--but the aesthetic value of the fonts is awfully elegant. Check out the full tear-down here.