Shirt Pocket Slide Rule: History of the HP-35

In a recently updated post, [Codex99] has a detailed history of the HP-35 pocket calculator. Unless you are a certain age, you probably don’t think much of calculators. They are cheap and not very essential in this day of cell phones and PCs. But in the 1970s they were amazing technology and the desire of every engineer and engineering student.

The story opens in 1965 when Tom Osborne — who was not an HP employee — build a floating point calculator he called the Green Machine. Apparently, he had painted the balsa wood case green. He had been showing it around but failed to get any interest until he showed it to Bill Hewlett. Hewlett wanted it to do trig functions and offered him a six-week consulting gig to work on improvements.

HP engineer Dave Cochran helped out and also helped envision making the device keystroke-programmable. By 1968, this collaboration led to a 40-pound desktop calculator — the HP 9100 — that was the size of a typewriter. It could be yours for only $4900. Keep in mind, that same amount would buy two brand new cars in 1968.

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