Remington EDC-III calculator (Sperry Rand)
This calculator was made in late 1968 and its "space-age" design (especially the graphics) is typical of that time: it could have come straight from "2001: A Space Odyssey".
The display uses miniature gas-discharge tubes ("Nixie tubes") which have ten wires inside them, one shaped like a "0", one shaped like a "1", and so on. This makes for a clear display but also means that different digits appear at different distances from the viewer: you can see this effect (which, on the whole, is fascinating rather than irritating) in the photograph.
The calculator is remarkable because it works to 20-digit precision - something that few other calculators have done, either before or since. Because there is room for only ten digits on the display, a rocker switch is provided which controls whether you are seeing the top 10 or the bottom 10 digits of the internal 20-digit display. A bright arrow (visible in the picture) warns you when the result is more than 10 digits long.
This example is in full working order and comes complete with a 24-page Operating Instructions booklet. You can read more about the EDC-III here.
This calculator has now been donated to the Science Museum.