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Sparking Innovation: HP-35 Calculator

December 26, 2015 Innovation Impact

HP-35 Scientific Calculator, 1973 THF159599

How did a shirt pocket lead to a feat of engineering?

The origins of Hewlett Packard’s HP-35 Scientific Calculator began with a challenge. In 1971, William Hewlett dared his engineers to prove their engineering prowess by miniaturizing the company’s 9100A Desktop Calculator—a forty-pound machine—into a device small enough to fit into a shirt pocket. The calculator’s target size of approximately 6x3 inches was supposedly arrived at by measuring one of Hewlett’s own shirt pockets.

The twelve or so experimental HP-35s that began as "company hacks" soon proved useful beyond the prototype stage. They were popular among the staff who built and tested them, and were presented for marketing studies. Despite a high manufacturing cost driving a retail cost of $395 (equivalent to $2200 in 2015), and research that warned of a limited market, Hewlett-Packard decided to proceed with production. The company’s 1972 sales goal of selling 10,000 calculators was quickly exceeded: they sold 100,000. Its rapid success made the slide rule obsolete practically overnight, as engineers, scientists, and mathematicians abandoned their analog calculating devices in favor of embracing the digital future.

The origins of Hewlett Packard’s HP-35 Scientific Calculator began with a challenge. In 1971, William Hewlett dared his engineers to prove their engineering prowess by miniaturizing the company’s 9100A Desktop Calculator—a forty-pound machine—into a device small enough to fit into a shirt pocket. Scientific American, Volume 227, July 1972-December 1972 THF126235

The HP-35 (named for its 35 keys) was the world’s first handheld scientific calculator. This advanced machine, with its full suite of features, was capable of processing more complex mathematical functions than any other calculator on the market at the time. It was also the company’s first product to use both integrated circuits and an LED display, which eased communication between the screen and keys. The HP-35 inspired others too—it caught the attention of a young Hewlett Packard engineer named Steve Wozniak. During the day, he worked at designing follow-up models of the calculator; in the evening, he developed his own electronic projects at home. All the while, he was percolating ideas towards the beginnings of the Apple 1 computer.

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