HP-35

HP-35. The HP-35 was the world's first handheld scientific calculator, introduced by Hewlett-Packard in 1972. Its name derived from its 35 keys, and it was marketed as a "slide rule for the electronic age," effectively making the slide rule obsolete for engineers and scientists. The device's ability to perform logarithmic and trigonometric functions portably revolutionized technical computation and cemented Hewlett-Packard's reputation in the electronics industry.

History and development

The project was initiated by Bill Hewlett after he observed engineers at Hewlett-Packard still relying on slide rules during a company retreat. He challenged the company's Corvallis, Oregon division, led by David Cochran and Tom Whitney, to create a pocket-sized version of their desktop HP 9100 calculator. The development team, which included key engineers like Malcolm McMillan, faced significant hurdles in miniaturizing components such as the read-only memory and designing a reliable keypad. The project was kept secret, known internally as "Project Colorado," and was launched at the Joint Computer Conference in 1972 to immediate acclaim, with initial demand far exceeding Hewlett-Packard's production forecasts.

Features and specifications

The device featured a full scientific calculator function set, including trigonometric functions, logarithms, exponentiation, and square root calculations, all accessible through its 35-key keyboard. It utilized a Reverse Polish notation entry system, which eliminated the need for parentheses and increased computational efficiency. The display was a 15-digit red LED screen capable of showing numbers in a scientific notation format with a two-digit exponent. Internally, it used three MOS Technology chips and had a four-register operational stack memory, all powered by a built-in rechargeable battery that allowed several hours of use.

Impact and legacy

The HP-35 had a profound and immediate impact on the engineering and scientific professions, rendering the slide rule obsolete virtually overnight and changing the standard practices in fields like aerospace engineering and applied physics. It established the handheld electronics market for professionals and spurred intense competition from companies like Texas Instruments and Commodore International. The success of the HP-35 directly led to the development of more advanced models like the HP-45 and the legendary HP-65, the first programmable pocket calculator. It is widely regarded as a landmark product in the history of computing, symbolizing the shift toward personal, portable computational power.

Technical details

The calculator's logic was implemented using three custom large-scale integration chips fabricated by MOS Technology, which were a significant innovation in integrated circuit design for consumer electronics. The CPU executed instructions stored in a read-only memory chip, while a separate chip drove the red LED display. The use of Reverse Polish notation for its logic was a deliberate design choice by the engineers, influenced by the work of Jan Łukasiewicz. The device's precise algorithms for functions like the CORDIC routine for trigonometric calculations were a major software achievement, ensuring both speed and accuracy within the constraints of its limited hardware.

Collectibility and value

The HP-35 is a highly sought-after item among technology collectors and historians of computing, with original units in good working condition commanding significant prices. Its value is influenced by factors such as the version number, with earlier "red dot" models and units with specific serial number prefixes being particularly prized. Fully functional examples with original accessories like the leather case and battery charger can fetch high sums at auctions conducted by entities like Christie's or on platforms such as eBay. The calculator is frequently featured in exhibits at institutions like the Computer History Museum and the Smithsonian Institution, underscoring its status as a pivotal artifact in the history of technology.