Curt Herzstark

Collectors and other cognoscenti of old calculating machines will immediately recognize this name as the inventor of the most famous and earliest mechanical pocket calculator, the Curta. The extraordinary story behind this invention is one of the most remarkable tales in the annals of the computing machine. The Curta literally saved Herzstark’s life. The story also shows the depravity to which human beings can sink.

Curt Herzstark was born on January 10, 1902, in Vienna, Austria. He was the son of Samuel Jacob Herzstark who was the founder and owner of the Vienna-based Rechenmaschinen-Werk “Austria” Herzstark & Co. The company had been in existence since 1905 and manufactured calculating machines and other precision instruments. The calculators produced by Austria were based on Thomas de Colmar’s Arithmometer (invented in the early 1820s and which itself was based on the earlier Leibniz calculator) which used the stepped drum principle. The company also sold office machines made by Burroughs and Remington. So the young Herzstark grew up in a world of calculators of different makes and models and sometimes in different stages of repair.

After finishing his high school education at the Realgymnasium in 1916, Herzstark joined his father’s company as an apprentice to become a precision mechanician and toolmaker. Following his apprenticeship he attended the Higher Technical School in Vienna to prepare himself further for a job as instrument maker. After graduating in 1922 he went back to the family business to learn the trade. His first assignment was to spend a year with the Astra company in Germany – also a manufacturer of adding machines – to learn the ins and outs of the production of these machines. Upon returning he began as a salesman and toured the country to demonstrate and sell the Austria calculators. That way he met many of the company’s clients himself. He soon noticed that many professional people, like builders, architects, bankers, etc. often expressed a desire to have access to a small portable calculator. Calculators in those times, like the Burroughs, Odhner and Arithmometer machines were large and heavy, simply unwieldy, not something one would take out into the field. As one customer expressed it “I can’t go back to the office just to add up a column of figures”. It soon made Herzstark think about how to design such a machine.

World War I censored express cover, cds Wien 19 VI 15, from the Herzstark company in Vienna to a bookshop in
Rotterdam, the Netherlands, with private advertising showing the Austria calculator. Arrival cds Rotterdam 21 VI 15.

The Curta

Manufacturers of existing adding machines and calculators had merely tried to shrink their machines, in other words reduce its size to a smaller version. Herzstark approached the problem from a different angle; he started with what today is called the “customer interface”. How would a potential customer use such a machine? Ideally he would hold the machine in one hand and operate the device with his other hand. The device should also be sturdy enough to operate in the field, say a building site, and even be able to survive a small fall. Not only did it have to be very accurate and easy to operate but it also had to support all four arithmetic functions – add, subtract, multiply and divide. If the device was handheld it should also be light enough to carry around easily and even fit in one’s pockets. Obviously these requirements put severe restrictions on its dimensions and weight. If you form a ring with your thumb and index finger, its diameter measures about 5-6 cm at best, while the width of a hand is less than 10 cm. These were the dimensions Herzstark kept as his guidelines. It wasn’t much if one keeps in mind that even the average beer can is larger at 11.5 by 6.4 cm.

Herzstark revolutionary design became possible because of his use of a single stepped drum to do all arithmetic. The top of his machine was used to display the revolution counter (i.e. how many times the crank had been turned) in black numbers on a white background and the results register showing white numbers on a black background. By rotating the whole top one notch, one would shift the position in the multiplier (= the revolutions counter) by one decimal place. The individual setting of the digits could be done by sliders on the side of the barrel-shaped calculator. The crank was situated on top as was a small ring which could be finger-pulled to zeroize the registers – similar to the modern pull-ring on a beer can. The problem of handling subtractions was dealt with in an ingenious way. Rather than turning the crank in reverse, like the Odhner and other stepped-drum calculators handled that problem, Herzstark realized that subtractions could be solved by adding the nine-complement of the number, adding “1” to the result and disregarding the leading “1” in the answer. He implemented this “add complement and add 1” solution as follows: the single stepped drum would have two sets of teeth, the lower set was used for the addition of numbers, while the second set (located 3 mm higher up) would be used for the addition of the nine-complement. Turning the crank normally engaged the lower set and added a number, while lifting the crank by just 3 mm engaged the second set of teeth and resulted in the addition of the number’s nine-complement followed by an automatic add of 1. It was pure brilliance.

Herzstark began the design process in the early 1930s. In 1937 Herzstark’s father passed away and Curt took over the running of the company. By the winter of 1937/38 he had a prototype of his revolutionary calculator ready – a machine that fitted comfortably in your hand, made soft whirring sounds when the crank was turned, had the shape of a miniature coffee grinder and operated in the same simple way – but the winds of war were gathering.

World War II

On March 10, 1938, the German Wehrmacht crossed the border of Austria – the infamous Anschluss – and life would never be the same again for Herzstark. Shortly after the invasion he managed to register two patents for his invention in Austria but further development and production of his calculators were made impossible. Although his father had been Jewish, his mother was a Catholic who later had become an Evangelical. This made Herzstark according to Nazi-Germany’s abhorrent race laws a half-Jew, an extremely precarious, if not deadly, position to be in. The Germans soon arrived to inspect the Herzstark factory and were impressed with the technical precision of the instruments produced. The company was instructed to stop all non-army work and to start producing gauges and other precision instruments for the Wehrmacht.

All went well until 1943 when two of Herzstark’s employees were arrested for listening to the English radio and translating and transcribing the broadcast using a typewriter. The employee owning the typewriter was summarily executed. When Herzstark was called as a witness he was immediately arrested for “helping Jews and subversive elements” and also for “indecent contact with Aryan women”. The last charge could easily have been raised if he had been seen kissing his mother. After his arrest he was put in a Vienna prison for Jews and subsequently deported to the Pankraz prison in Prague where he had to share a cell with 50 other inmates without beds or ablution facilities and where torture had become a habit. Finally he was sent to concentration camp Buchenwald.


Buchenwald concentration camp was located near Weimar in East Germany and had been in operation since 1938. More than 50,000 prisoners died there under the brutal Nazi regime through shooting, hanging, starvation, medical experiments and general hardship. When the American forces liberated the camp on April 11, 1945, only 21,000 survivors were found, in the most deplorable conditions.

It was in this death camp that Herzstark arrived in 1943. Initially he was ordered to do gardening, a heavy and exhausting job for him and soon his health started deteriorating. Due to the fact that the Herzstark company had worked for the Wehrmacht he was defined as an “intelligence-slave” (a semi-protected position for all prisoners with technical expertise and skills who could serve the German Reich). One day the SS-commander called him to his office and told him that if he followed their orders obediently he would be sent to the Gustloff factory which adjoined the concentration camp. This factory was producing high-precision mechanical instruments, parts and tools for the German war machine – an environment where his life would be slightly more bearable. Herzstark’s health soon improved and he even managed to help out his co-prisoners with the occasional item of food. He was also instructed to produce a calculating machine to be presented to the Führer after Germany had won the war. Obviously Herzstark saw this as his ticket to survival. He started to reproduce the drawings for his Curta from memory using a drawing board made available to him. He was only allowed to work on his project on Sundays and after hours. He spent all his spare time meticulously drawing the design in pencil and when Buchenwald was finally liberated in April 1945 he had virtually completed the drawings.

After the war

With the drawing in his pocket, Herzstark approached the Rheinmetallwerke factory in Sömmerda near Weimar. The drawings were so complete and detailed that within eight weeks three prototypes of the Curta I had been produced. Rheinmetallwerke were so enthusiastic about the new calculator that they started drawing up a contract with Herzstark for the production of his invention. However, following the Potzdam agreement the Weimar area had become part of the Russian occupation zone and when the Russians started to arrive, Herzstark suspected that he, like many skilled workers before him, might soon be deported to Russia. He took his drawings, his three prototypes (which still exist today), dismantled them completely, put the parts in a box so it looked like the parts of a child’s toy and traveled back to Vienna, Austria, where he arrived in December 1945. Unwilling to continue in the original Herzstark factory, which his younger brother Ernst had been running and who now demanded a share in Curt’s invention if it went in production there, he contacted the Swiss typewriter and calculator company Jost. While negotiations with Jost were still in progress, Herzstark was contacted by Prince Franz Josef II of the Principality of Liechtenstein who sought to modernize the post-war manufacturing industry in his country. Liechtenstein is a tiny country (only 61 square miles) located in the Alps between Austria and Switzerland. As this was a much more lucrative offer, Herzstark grabbed the opportunity and a factory was built in Mauren in Liechtenstein. The company operated under the name Contina AG with Herzstark being its technical director and a 35% share holding. In the meantime Herzstark managed to register his patent in the USA - Patent 2,525,352, January 9, 1948. The first Curta calculators were produced in Liechtenstein in the autumn of 1948. All models came in black only and fitted snugly in your hand. The Curta operated smoothly and felt comfortable; it came in its own sturdy protective case with rubber lining on the inside to protect the machine against mishaps. When Contina AG got into funding problems it tried to negotiate a new contract with Herzstark. He soon realized that ending the AG would also leave his 35% share holding worthless. Fortunately Contina had never registered the original Herzstark patents in their name – that way they would not be held liable if things went wrong – and Herzstark and Contina parted company. Because he was still the owner of the patents, the company was forced to continue production of the Curtas – finally his invention brought him some money. Herzstark continued as a free-lance consultant for a while but this soon stopped. In 1966 Contina was bought by the Hilti company but after the first electronic calculators arrived on the scene in the late sixties Hilti stopped the production of Curta machines in 1972. In total just over 140,000 Curta machines had been manufactured.

Herzstark withdrew from public life and hardly anything was heard from him since. In 1987 the Charles Babbage Institute at the University of Minnesota conducted an in-depth interview with Herzstark, who by then was 85 years of age – together with Konrad Zuse the only two designers of mechanical calculators still alive at that time.

Curt Herzstark died on October 27, 1988 in Nendeln in the Principality of Liechtenstein.

From Liliput to Curta I and Curta II

On his design drawings Herzstark had indicated the name of his new calculator as the Liliput. The same name featured on the first prototypes. However, Contina AG didn’t like the name and Herzstark recalled that during the trade fair in Basel in 1948 one of the Contina trade correspondents, the Dutch Miss Ramakers, mentioned that the calculator was the daughter of Mr. Herzstark. “When the father is called Curt, the daughter has to be called Curta.” That’s when its name changed from Liliput to Curta.

The first Curta model, the Curta I, had a capacity of 8x6x11, meaning a setting register of 8 positions for the multiplicand, 6 positions in the revolutions register for the multiplier and 11 positions in the results register. For its measurements and other details, see the following table.
The larger version, the Curta II, was produced from 1954 onwards and had a capacity of 11x8x15.


Curta I

Curta II>


stepped drum

stepped drum


8 x 6 x 11

11 x 8 x 15

Production years

1948 - 1970

1954 - 1972

Machines manufactured

about 80,000

about 61,000

Serial number range

1 – 80,000

starts with 500,000


Ø 53 mm

Ø 65 mm


85 mm

90 mm


230 gr.

360 gr.

Number of parts




all black

black with red setting knobs

Early car rally enthusiasts had a soft spot for the Curta. It was small enough to be held while driving during a rally, it could be operated virtually by touch only, reliable enough to withstand dust and bumps, in short the ideal on-board machine to accurately calculate speeds, driving times and distances.

Even today the Curta calculator is still a remarkable marvel of technology and many collectors of mechanical calculators consider a Curta, especially the older Curta I, a prized possession. While in 1960 a Curta 1 carried a price tag of $125, currently a vintage Curta 1 in good condition may well set you back $1,000.

Although Herzstark has never been portrayed on a stamp, the Principality of Liechtenstein has honored him by issuing a stamp on 20-11-2006 featuring his invention showing a drawing and a photograph of the famous Curta – a Curta II model. A wonderful tribute to a remarkable man.

© Wobbe Vegter, 2008

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