Enlarge / The Curta mechanical calculator.
It’s no bigger than a drinking glass, and it fits easily in the palm of the hand. It resembles a pepper grinder—or perhaps a hand grenade.
The diminutive “Curta” is a striking machine, a mechanical calculator that combines the complexity of a steamship engine and the precision craftsmanship of a fine pocket watch. It first appeared in 1948, and for the next two decades—until it was displaced by the electronic calculator—it was the best portable calculating machine on the planet. And its story is all the more compelling in light of the extraordinary circumstances in which it was invented.
The idea of the Curta came to its Austrian-born inventor in the darkness of the Buchenwald concentration camp.
“Isn’t there anything smaller?”
Today, we take number-crunching for granted. Our smartphones have calculator apps, and most of us have a pocket calculator somewhere in our home or office. But it wasn’t always so easy. For centuries, anything more than simple addition was painfully time-consuming. The first slide rules appeared in the 17th century, not long after John Napier’s invention of the logarithm, but they could only handle a couple of positions beyond the decimal place. There were also various kinds of mechanical adding machines, but most were crudely built and unsuited to scientific work. By the late 19th century, more reliable desktop calculators began to appear, but they were heavy and expensive.
The shortcomings of these machines were very much on the mind of the young Curt Herzstark, whose family was in the business of making and selling calculating machines and other office equipment. Born in 1902 in Vienna, Herzstark was running the family business by the 1930s. He traveled extensively across Austria, Hungary, and Czechoslovakia, selling mechanical calculators to banks and factories. Advertisement
Thanks to an extensive interview conducted for the Charles Babbage Institute many years later, we have Herzstark’s own recollections of those busy years. He recalled that as sophisticated as his company’s machines were, “something was missing in the world market.” He remembered meeting with architects, foremen, and customs officers who needed calculating machines that were not only accurate and reliable but also portable.
“People said again and again, ‘Yes, that is nice, but isn’t there anything smaller?’” Herzstark recalled. Slide rules were not good enough; his customers wanted precise figures, not approximations. Simply taking existing designs and making all of the various parts smaller wouldn’t do the trick; the keys and knobs would be too small to use. A radical redesign was needed.
“What does this kind of machine really have to look like so that someone could use it? It cannot be a cube or a ruler; it has to be a cylinder so that it can be held in one hand,” Herzstark mused. “And if one can hold it in one hand, then if it is miniaturized, you could adjust it with the other hand… I started to design the ideal machine from the outside first, before I designed the insides.”
Herzstark began to experiment with “sliders” that wrapped around a cylinder so that numbers could be entered by moving a thumb or finger. He also reasoned that there only needed to be a single calculating mechanism, so long as each input …….