Alex's Adventures in Numberland - Alex Bellos [82]
Throughout the 1950s and the 1960s the Curta was the only pocket calculator in existence that could produce exact answers. But both the Curta and the slide-rule were all but rendered extinct by an event in the history of arithmetical paraphernalia as cataclysmic as the meteorite that is said to have annihilated the dinosaurs: the birth of the electronic pocket calculator.
It is hard to think of an object that has disappeared so quickly after such a long period of dominance than the slide-rule. For 300 years it reigned supreme until, in 1972, Hewlett-Packard launched the HP-35. The device was promoted as a ‘high precision portable electronic slide-rule’, but it wasn’t like a slide-rule at all. It was the size of a small book with a red LED display, 35 buttons, and an on-off switch. Within a few years it was impossible to buy a general-purpose slide-rule except second-hand, and the only people interested in them were collectors.
Even though the electronic calculator killed off his beloved slipstick, Peter Hopp bears no grudge. He likes to collect early electronic calculators too. When our conversation moved to them, he showed me his HP-35, and started reminiscing about the time he first saw one in the early 1970s. At the time, Hopp was beginning his career at Marconi, the electrical communications firm. One of his colleagues had bought an HP-35, which had cost him £365 – at the time, about half the annual salary of a junior engineer. ‘It was so valuable he kept it locked in his desk and never let anyone use it,’ Hopp said. The colleague, however, had another reason for his secrecy. He believed he had found a way of using the calculator that could save the company 1 percent of its expenditure. ‘He had top-secret meetings with the bosses. It was all hush, hush,’ said Hopp. In fact, though, his colleague had made a mistake. Calculators aren’t perfect instruments – type in 10 and divide by 3. You get 3.3333333. Multiply the result by 3, however, and you do not get back to where you started; rather, you get 9.9999999. Hopp’s colleague had used what was an anomaly in digital calculators to create something from nothing. Hopp recalled the incident with a smile: ‘When the plan was peer-reviewed by someone who used a slide-rule, the improvements were judged illusory.’
The story demonstrates why Hopp laments the demise of the slide-rule. The device provided the user with a visual understanding of numb which meant that even before he had worked out the answer he had a rough idea of what it would be. Nowadays, Hopp said, people plug numbers into a calculator without any intuitive sense of whether the answer is correct.
Still, the digital electronic calculator was an improvement on the analogue slide-rule. The pocket calculator was easier to use, gave precise answers and by 1978 was priced under £5, making it accessible to the general public.
It is now more than three decades since the slipstick slipped away, which means it is surprising to discover that there is, in fact, one situation in the modern world where they are still commonly used. Pilots use them to fly planes. A pilot’s slide-rule is circular, called a ‘whizz wheel’, and measures speed, distance, time, fuel consumption, temperature and air density. In order to qualify as a pilot, you must be proficient with a whizz wheel, which seems utterly strange, bearing in mind the high-end computer technology now used in cockpits. The slide-rule requirement