Ptak Science Books: Mechanical Calculating Pencil, 1876
Ptak writes:
I've seen a number of unusual calculating machines, but this one--patented by Marshall Smith in 1876) seems one of the smallest, and efficient--if not limited--varities. It is the second edition so-to-speak of a mechanical, graphite pencil, operating this time without rotors or any other internal mechanical devices. It was evidently a big seller--hosted in part, so it seems, by The Scientific American itself--having sold some 5,000 units.
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