Hewlett Packard HP-35
The HP-35 was Hewlett-Packard's first pocket calculator and the world's first scientific pocket calculator (a calculator with trigonometric and exponential functions). Like some of HP's desktop calculators it used reverse Polish notation. Introduced at US$395, the HP-35 was available from 1972 to 1975.
Market studies at the time had shown no market for pocket sized calculators. In about 1970, HP co-founder Bill Hewlett challenged his co-workers to create a "shirt-pocket sized HP-9100". Thus, the first 12 HP-35 portable calculators were made as a "hack" by and for other engineers at HP. It is rumored that the development engineer got carried away and implemented a full suite of scientific functions to satisfy requests from his co-workers. When these prototypes proved popular, HP decided to turn the HP-35 into a commercial product. The HP-35 was the first calculator with a full suite of trigonometric and transcendental functions.
In the first months orders were exceeding HP's expectations as to the entire market size, which was 10,000 units per year. Before the HP-35, the only practical portable devices for performing trigonometric and exponential functions were slide rules. Existing pocket calculators at the time were only four-function, i.e., they could only do addition, subtraction, multiplication, and division. It had been originally known simply as "The Calculator", but Hewlett suggested that it be called the HP-35 because it had 35 keys.
The HP-35 was exactly 5.8 inches long and 3.2 inches wide. This was the size of William Hewlett's shirt pocket, hence "pocket calculator".
It was the first scientific calculator to fly in space (along with the HP-65 and HP-41) in 1972
It was the first pocket calculator with a numeric range that covered 200 decades (10+/-100)
The LED display power requirement was responsible for the HP-35's short battery life between charges — about three hours. To extend operating time and avoid wearing out the on/off slide switch, users would press the decimal point key to force the display to illuminate just a single LED junction.
The HP-35 calculated arithmetic, logarithmic, and trigonomic functions but the complete implementation used only 767 carefully chosen instructions (7670 bits).
Introduction of the HP-35 and similar scientific calculators by Texas Instruments soon thereafter signaled the demise of the slide rule as a status symbol among science and engineering students. Slide rule holsters rapidly gave way to "electronic slide rule" holsters, and colleges began to drop slide-rule classes from their curricula.
100,000 HP-35 calculators were sold in the first year, and over 300,000 by the time it was discontinued in 1975—3½ years after its introduction
IEEE, the world’s largest technical professional association, announced that it has named the HP-35 scientific calculator as an IEEE Milestone. Introduced in 1972, the HP-35 was the world’s first handheld-sized scientific calculator which ultimately made the slide rule, which had previously been used by generations of engineers and scientists, obsolete.
Our HP-35 calculator has a reference number of 00035-90008 and is complete with manual, power supply, adapter, hard and soft case. This was very kindly donated to The Centre For Computing History by Aubrey Thyer