Mechanical pocket calculator: A Curta Type II, constructed from 1953 onwards.
Mechanical pocket calculator: A Curta Type II, constructed from 1953 onwards. Wikimedia / National Museum of Computing, Bletchley Park

Numbers in a can: the ‘Curta’ handheld calculator

‘A sturdy, high-performance assistant for all four types of calculation, right there in your pocket’, promised the sales brochure. The world’s smallest handheld mechanical calculator was made in Liechtenstein.

Thomas Weibel

Thomas Weibel

Thomas Weibel is a journalist and Professor of Media Engineering at the Fachhochschule Graubünden and the Hochschule der Künste in Berne.

Prologue: Precision engineer Christophe Clément was a big fan of mechanical calculating machines. In 1987, in his first year of studies at what was then the Ingenieurschule Freiburg (Fribourg School of Engineering), he asked about the extremely compact calculating machines which he knew had been loaned to students for a fee of 20 francs a year until the 1970s – but his enquiries proved fruitless. After the rise of the electronic pocket calculator, these ‘Curta’ calculators, the smallest mechanical calculators in history, had sunk into oblivion and were lost.
Precision engineer Curt Herzstark (1902-1988) was the son of Austrian Jewish businessman Samuel Jacob Herzstark, who in 1905 had set up Austria’s first calculator factory, the ‘Austria’ calculating machine plant. From a young age little Curt was tinkering and making things in his father’s workshop, and he accompanied Herzstark Senior to international office equipment trade fairs. The young Herzstark completed an apprenticeship as a toolmaker and precision engineer at the ‘Austria’ factory; he became an engineer and dreamed of developing a calculating machine so compact that it could be carried in a pocket. What he had in mind wasn’t a miniaturisation of existing devices, but a completely new design of small calculator. ‘A slide rule made no sense,’ said Herzstark in an interview in 1987: ‘First of all, you can’t add and subtract with it, and what’s more you can only get approximate values with the cursor. (…) But I wanted to know the exact value.’
Bigger than the ‘Curta’ and designed to perform just one arithmetical operation: the ‘CONTO’ adding calculator, a Swiss product, around 1935.
Bigger than the ‘Curta’ and designed to perform just one arithmetical operation: the ‘CONTO’ adding calculator, a Swiss product, around 1935. Swiss National Museum
Curt Herzstark at the age of 8 using an Austria Model III during the International Office Exhibition in Vienna in 1910.
Curt Herzstark at the age of 8 using an Austria Model III during the International Office Exhibition in Vienna in 1910. Wikimedia
In 1939, his dream began to take shape. His design was the shape of a small tin can and was a convenient cylinder weighing 230 g, with a diameter of just 5.3 cm and standing 8.5 cm high. It was operated with a series of sliders around the sides and, to trigger the calculation process, a smooth crank handle on the top. The device could perform all four basic operations in numbers up to 11 and, later on, 15 digits, and even rule-of-three calculations and square roots were possible. Herzstark applied for the first patents before the start of World War II. But then global politics put a spoke in the inventor’s wheel. In July 1943 Curt Herzstark was arrested as a ‘half-Jew’, and after stints of imprisonment in Vienna, Linz and Budweis (České Budějovice) he was taken to Buchenwald concentration camp. Initially a forced labourer in the camp market garden, he became seriously ill. ‘That was a really nasty business,’ Herzstark said later, ‘how I was brought to Buchenwald. Mentally I was at rock bottom.’ But his supervisors soon noticed his talent for precision mechanics, and he was transferred to the Wilhelm Gustloff Werke, an SS precision engineering factory. Here, Herzstark became head of the precision parts department, which produced components such as those required for Germany’s V2 rocket.
Gate to Buchenwald concentration camp.
Gate to Buchenwald concentration camp. Wikimedia / Andreas Trepte
In his free time, on Sunday mornings and late in the evening, he produced design drawings for his calculator, provisionally named ‘Herzstark Liliput’. The camp commandant hoped one day to personally present one of the machines to Adolf Hitler. As a department head, Herzstark saved the lives of many fellow prisoners, by employing them in his department: his special status allowed him to receive food parcels and to bring other concentration camp inmates into the sheltering environment of the factory. After the war, he was awarded the Order of the Luxembourg Brotherhood for rescuing a Luxembourg worker.
Curta Type II, constructed from 1953 onwards.
Curta Type II, constructed from 1953 onwards. Swiss National Museum
After his liberation by troops of the US 3rd Army in April 1945 and the handover of Thuringia to the Soviet occupying forces, Herzstark fled to Vienna with the plans for his mini calculator. In the Austrian capital he looked for business partners with the backing of whom he hoped to start mass production of his new device – unsuccessfully. His correspondence with American and Swiss precision machine manufacturers also came to nothing. He finally found a mentor in Prince Franz Josef II, in the Principality of Liechtenstein: ‘It was disclosed to me that the Prince of Liechtenstein wished to build up the country’s industry and was seeking experts in the field, and it had been discovered through thorough enquiries that I was the right man,’ Herzstark later said. There was just the question of the name. The marketing people suggested ‘Liliput’ was too exotic, and the meeting started to get out of hand. Finally the secretary piped up: ‘Gentlemen, I don’t understand this argument. The inventor’s name is Curt, and this is his daughter. Why don’t we just call her “Curta”?’ With that, the brand name was born.
Instruction manual for the ‘Curta’.
Instruction manual for the ‘Curta’.
Disassembly instructions from the service manual for the ‘Curta’.
Disassembly instructions from the service manual for the ‘Curta’.
In 1946 Contina AG was founded in Mauren, Liechtenstein. From 1948 to 1970, the company produced a total of around 140,000 units of the calculator that bore its designer’s name. Despite the high price of 425 German marks in 1965 (around 1,000 Swiss francs today), the ‘Curta’ was a huge success. In the 1970s, however, the electronic pocket calculator began its inexorable rise, and the mechanical ‘Curta’ gradually fell by the wayside. Epilogue: In 1987, nobody at the Fribourg School of Engineering could remember where the tiny mechanical calculators were. But the student Christophe Clément persisted, and finally one day a secretary opened a long-forgotten drawer and voilá – there were a dozen of the pepper grinder-like devices. The director, who had himself been looking for the missing ‘Curtas’ for a long time, was elated. As a gesture of gratitude, he offered the finder one of the devices – for a symbolic payment of 50 francs. Today, Clément is the proud owner of a whole collection of mechanical calculating machines. In pride of place is a fully functioning ‘Curta’, one of those marvels of precision engineering created by the inventor Curt Herzstark.
Tip: At the ENTER Museum of Computer and Consumer Electronics in Solothurn, along with original ‘Curta’ models you can also explore a wooden model that shows how the calculating machine worked.
How the ‘Curta’ works. YouTube

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