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The Pocket Calculator

Abstract

For 350 years the slide rule was the engineer’s portable computer. Between 1971 and 1976 it was retired by a shirt-pocket gadget. The electronic pocket calculator arrived from Japan, was made possible by the same silicon that produced the first microprocessor, and set off a price war so fast that four-function models fell from hundreds of dollars to a few dollars in five years. Hewlett-Packard’s HP-35 killed the slide rule for scientists in 1972; Texas Instruments then killed the high price. Most of the companies that started the race, including the one that gave America its first pocket calculator, did not survive it.

The Prototype Nobody Could Sell Yet

The pocket calculator began at Texas Instruments as a demonstration that a calculator could be small. In 1967 a team led by Jack Kilby, co-inventor of the integrated circuit, built the “Cal-Tech” prototype: a battery-powered handheld that could add, subtract, multiply, and divide, printing results on a strip of thermal paper. It was heavy, it was slow, and TI had no intention of selling it. The point was the patents. TI filed for master patents on portable electronic calculators and then waited for the components to get cheap enough to matter.

The first products to reach shops came from Japan. Sharp, Sanyo, and Canon shipped portable calculators in 1970, most of them still too large and too expensive for a pocket in any honest sense. Canon’s Pocketronic used the TI Cal-Tech design and printed on paper tape rather than showing digits on a display.

The First One That Fit

The machine that earned the name arrived in early 1971. The Busicom LE-120A “HANDY” was the first calculator small enough to carry in a pocket, the first to use a light-emitting-diode display, and the first to run on a single integrated circuit and replaceable AA batteries. Busicom is the more consequential name in this story for a second reason: it was Busicom that had commissioned Intel to build a set of calculator chips, and Intel’s engineers answered by putting the logic on one general-purpose part, the Intel 4004. The microprocessor was born as a way to build calculators (see Federico Faggin and the Microprocessor). Busicom, short of cash, traded away its exclusive rights to the chip in exchange for lower prices, and the 1974 recession in Japan made it the first major Japanese calculator maker to fail. Intel kept the microprocessor.

America’s first pocket calculator came from an Indiana instrument maker. Bowmar put the 901B, nicknamed the “Bowmar Brain,” on sale in autumn 1971: eight red LED digits, four functions, $240. It sold well enough that Bowmar could not keep up, which turned out to be the wrong problem to have.

The Slide Rule Killer

None of these could do the work an engineer actually needed. They added and multiplied; they could not take a sine or a logarithm. For that an engineer still reached for the slide rule, the two-scale device William Oughtred had assembled around 1622 and that had sized bridges and flown to the Moon on Apollo (see Before the Computer: Mechanical Calculation).

Bill Hewlett changed that on a whim. He had watched customers buy HP’s desktop 9100A and wanted the same power in a shirt pocket, so he measured his own shirt pocket and told his engineers to build a calculator that fit. The HP-35 shipped in 1972 at $395. It was the first handheld calculator with trigonometric and exponential functions, the first that a scientist could carry instead of a slide rule (see Hewlett-Packard). The market research said not to build it: a Stanford Research Institute survey recommended against the product, and the most optimistic forecast ran around 1,000 units a month. It sold 100,000 in the first year and more than 300,000 by the time it was discontinued in 1975. HP-35s flew on the Skylab 3 and Skylab 4 missions.

The effect on the slide rule was quick and total. Colleges stopped teaching it; slide-rule makers stopped making it. A tool that had lasted three and a half centuries was gone from engineering practice inside a decade.

The bug HP told everyone about

An early HP-35 had a flaw in its transcendental-function code: certain calculations, such as raising e to the logarithm of 2.02, returned 2 instead of 2.02. HP had already sold some 25,000 units when the bug surfaced. In the meeting about what to do, someone suggested not telling; Dave Packard’s pencil snapped, and HP wrote to the owners it could reach, explained the error, and offered a replacement to anyone who wanted one. Many customers, told their expensive calculator was flawed, chose to keep it anyway.

The Price War

Texas Instruments had the patents, the chips, and a reason to stop merely licensing to everyone else. In 1972 it entered the market directly with the Datamath, a four-function calculator, and then did to the calculator what it had spent years preparing to do: drive the price down until competitors could not follow. Because TI made its own integrated circuits, it could undercut companies that had to buy theirs.

The numbers fell at a speed the industry had never seen. In Britain, Clive Sinclair shipped the Sinclair Executive in September 1972 as the first genuinely slim pocket calculator, then the Sinclair Cambridge in August 1973 at £29.95 plus VAT, or £24.95 as a build-it-yourself kit; by late 1974 the mail-order price had fallen to £16.95. Casio pushed volume from Japan. By 1976 the cheapest four-function calculator cost a few dollars, about one-twentieth of the 1971 price. The device that had been a status symbol in 1971 was a giveaway by 1976.

The companies that had started the race were the ones it crushed. Bowmar, which had given America its first pocket calculator and depended on buying chips from TI, was squeezed between rising demand and falling prices and filed for bankruptcy in 1976. Commodore survived the calculator business only by buying its own chip supplier, MOS Technology, whose 6502 processor would later run the personal computers of the next decade. The calculator war killed more than the slide rule. It selected, brutally, for the handful of firms that owned their silicon.

The Model That Ended the Argument

Texas Instruments closed the scientific-calculator market the same way it had closed the four-function one. In 1976 it released the TI-30, a scientific calculator with the functions of an HP-35, for about $25 when HP’s cheapest scientific model still cost well over $100. It sold an estimated 15 million units between 1976 and 1983, which made it the best-selling calculator of its era and put a machine capable of trigonometry into the hands of essentially every science student. What had been a $395 professional instrument in 1972 was, four years later, a classroom staple that cost less than the textbook next to it.

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