Design blog Codex 99 has published an image-filled piece on Hewlett-Packard's HP-35 scientific calculator, telling the story of how the revolutionary device became a design classic. The key to the creation of the calculator — which cost a whopping $395 at its 1972 launch but sold in record numbers — was an outside-in approach, with designers constructing the outer shell and user interface before attempting to fill it with working parts. Thankfully, the technology proved cooperative, and HP was able to produce the first in a line of pocket-size computing devices that, as Codex 99 points out, stretches all the way to today's smartphones. Check out the post for more classic HP-35 pictures, including press shots and one of the original design documents.