A curious slide rule design

For some reason, inventors in the first half of the 20th century thought that incorporating a slide rule into a mechanical pencil was a great idea. In reality, these combination devices were of dubious utility, gives their low precision as calculators… but they are certainly ingeniously designed.

Pencil Sliderules

I describe three of them,  including one extremely rare device, in a new article on my history of computing site.

Enjoy!

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