It was the fall of 1965 and Jack Kilby and Patrick Haggerty of Texas Instruments sat on a flight as Haggerty explained his idea for a calculator that could fit in the palm of a hand. This was a huge challenge since at that time calculators were the size of typewriters and plugged into wall sockets for their power. Kilby, who’d co-invented the integrated circuit just seven years earlier while at TI, lived to solve problems.
By the time they landed, Kilby had decided they should come up with a calculator that could fit in your pocket, cost less than $100, and could add, subtract, multiply, divide and maybe do square roots. He chose the code name, Project Cal Tech, for this endeavor, which seemed logical as TI had previously had a Project MIT.
Rather than study how existing calculators worked, they decided to start from scratch. The task was broken into five parts: the keyboard, the memory, the processor, the power supply, and some form of output. The processing portion came down to a four-chip design, one more than was initially hoped for. The output was also tricky for the time. CRTs were out of the question, neon lights required too high a voltage and LEDs were still not bright enough. In the end, they developed a thermal printer that burned images into heat-sensitive paper.
Just over twelve months later, with the parts all spread out on a table, it quietly spat out correct answers. A patent application was filed resulting in US patent 3,819,921, Miniature electronic calculator, which outlined the basic design for all the calculators to follow. This, idea borne of a discussion on an airplane, was a pivotal moment that changed the way we teach every student, and brought the power of solid-state computing technology into everyday life.
TI showed the Cal Tech prototype to a number of companies and Canon took an interest. Canon brought it to market as the Pocketronic, releasing it in Japan in October 1970 and the US in April 1971, selling for around $150 ($910 in 2017 dollars). It had three chips and a heat-sensitive paper tape readout. It was still just handheld though, not really pocket-sized, but sold very well.
By then a number of other handheld calculators were also hitting the market. In November 1970, the first calculator-on-a-chip, the Mostek MK6010, was announced, followed in February 1971 by the first truly pocket-sized calculator, the Busicom LE-120A “Handy” that used the chip. That same year, TI followed with their own calculator-on-a-chip and in 1972 TI started releasing its own calculators.
In 1972 Hewlett-Packard released the HP-35, the first scientific calculator, one that could replace a slide rule. It used reverse Polish notation (which our own [Jenny List] recently wrote about), included scientific notation and had 35 buttons, hence its name. Despite a $395 price tag ($2,320 in 2017), 100,000 were sold in its first year. The HP-35, along with the release of TI’s equivalent SR-50 in 1974 for $150, spelled the end of the actual slide rule. (The SR stood for Slide Rule.)
Display technology also advanced through vacuum fluorescent displays, LEDs and LCDs. In the mid-1970s, twisted nematic (TN) LCDs gave calculators the now omnipresent dark numerals on a light background while decreasing the power requirements to the point where they could run on button cells.
Prices dropped as new features were added and sales doubled each year. By 1976, a four-function calculator cost only a few dollars. In 1972, 5 million calculators were sold in the US and within ten years there were more calculators in the US than people.
Why had the calculator become so popular? This was a clear case of a consumer product that was conceived for a market that wasn’t known to exist. When Haggerty conceived of the idea in 1965, calculators were heavy and took up significant space on a desktop, so perhaps the convenience of one which you could carry around played a part. They also needed no setup, no programming — simply flip the on/off switch and do some calculations. For the average person, they replaced the need to learn multiplication tables, necessary for working out how much a dozen apples would cost at $0.05 an apple. They also made it easier for the high school student to do the trigonometry in their physics homework. Though, in the early 1970s, given the initial high price, perhaps it was engineers and companies that bought them first.
I can attest to the latter. I was just becoming a teenager back around 1976 when my father bought a TI-30 calculator for $25, or around $107 in 2017 dollars. The mining company at which he worked as an electrician had made them available. Before that, I recall using long division to divide up a long sheet of paper for a mural that was to be a backdrop for a school play. I would likely have gone on to learn to use a slide rule, but never did. After the calculator arrived, I’ve done long division on paper only once when no calculator was available, though I have done it for fun and to see if I remember how.
Through the decades that followed, calculators continued to gain functionality. In 1974, HP came out with their first programmable calculator, the HP-65. It had 100 functions and stored programs with a magnetic card reader. Starting in 1978, a company called Calculated Industries released very niche calculators such as the Loan Arranger for the Real Estate industry with functions for calculating payments and future values. Then later came the Construction Master with programmed functions for pitch, rise, run, feet-inch conversions and more. In the 1990s TI came out with the TI-81, a popular graphing calculator for algebra and precalculus courses and power by a Zilog Z80.
If memory serves, it was a programmable Sharp El-5040 with a single line formula display that I’d left behind in a University auditorium, hopefully having found a good home on an engineer’s desk. Now, my Sharp EL-531W, also with a single line formula that can be retrieved and edited, sits ever-present beside my computer monitor, getting daily use while a Casio fx-3600P that I’d thought I’d lost but later found, sits waiting for its turn in my desk drawer.
This being Hackaday, you no doubt have a calculator that gets frequent use. Or perhaps you have your own fond memories of one that got away or a family one that you grew up with. Or perhaps there’s one you’ve hacked, like this ESP8266-connected scientific calculator? Share your stories with us, we’d love to hear how the calculator has played a part in your life. We also wonder how much longer the calculator as a distinct piece of electronics will survive now that the infinite adaptability of smartphones has made calculator apps the go-to for today’s upcoming engineering candidates?
[Pocketronic photo used in main image via Dentaku-Museum]