History Software Engineering

HP-35 Calculator – 1972 AD

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HP-35 Calculator

Bill Hewlett (1913–2001), David Packard (1912–1996)

Founded in a Palo Alto garage by Bill Hewlett and his Stanford classmate David Packard in 1939 with just $538, Hewlett-Packard (HP) was a respected manufacturer of test equipment for the electronics industry by 1950. The company introduced its first computer in 1966, and a programmable desktop calculator with a screen, printer, and magnetic card storage in 1968 that cost $4,900.

In 1968, Bill Hewlett decided that HP should create a portable electronic calculator that would fit in a shirt pocket. Hewlett was positive such a product would be successful, even though HP’s marketing department did not see a need for it, arguing that the company’s desktop calculators were selling just fine. But the project went ahead per Hewlett’s wishes and in 1972 was introduced to the public.

Hewlett’s idea was to build a portable calculator, powered by three AA batteries, using new integrated circuits from Intel and two other vendors, and have it show results on a single-line display made from light-emitting diodes. Inside, the calculator was powered by a microprocessor running at 200 kilohertz with a program that was just 768 instructions long. As the device’s manual stated, “Its ten digit accuracy exceeds the precision to which most of the physical constants of the universe are known.”

Just as much thought and care went into the design of the physical shell. The plastic keys were manufactured with a special two-step process so that the numbers could not rub off. Designed to survive a 3-foot drop onto concrete, the calculator was praised for its strength and reliability. Reportedly, HP’s sales representatives would drop and even throw the calculators to demonstrate how tough they were.

From its launch, the $395 calculator took the market by storm—even at a time when the average month’s rent in the United States was just $165. The company needed to sell 10,000 units to break even; it sold 100,000 in the first year. HP’s calculator singlehandedly destroyed the market for slide rules.

Originally called just “the calculator,” it was renamed the HP-35 (because it had 35 keys) in 1973, after HP started selling a portable business calculator, the HP-80. Confusingly, the HP-80 also had 35 keys.

SEE ALSO Slide Rule (1621), Thomas Arithmometer (1851), First LED (1927), Curta Calculator (1948), ANITA Electronic Calculator (1961)

The HP-35 calculator, the world’s first handheld scientific calculator. Note the π (pi) button.

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