thumb|Curta Type I, on display at the [[Musée des Arts et Métiers, Paris.]]

thumb|upright=1.8|A partially disassembled Curta calculator, showing the digit slides and the stepped drum behind them

thumb|Curta Type I calculator, top view

thumb|Curta Type I calculator, bottom view

The Curta is a hand-held mechanical calculator designed by Curt Herzstark.

Curtas were considered the best portable calculators available until they were displaced by electronic calculators in the 1970s. This single drum replaced the multiple drums, typically around 10 or so, of contemporary calculators, and it enabled not only addition, but subtraction through nines complement math, essentially subtracting by adding. The nines' complement math breakthrough eliminated the significant mechanical complexity created when "borrowing" during subtraction. This drum was the key to miniaturizing the Curta.

His work on the pocket calculator stopped in 1938 when the Nazis forced him and his company to concentrate on manufacturing precision instruments for the German army.

Herzstark, the son of a Catholic mother and Jewish father, was taken into custody in 1943 and eventually sent to Buchenwald concentration camp, where he was encouraged to continue his earlier research:

In the camp, Herzstark was able to develop working drawings for a manufacturable device. Buchenwald was liberated by U.S. troops on 11 April 1945, and by November Herzstark had located a factory in Sommertal, near Weimar, whose machinists were skilled enough to produce three working prototypes. These were the same people who had earlier elected not to have Herzstark transfer ownership of his patents to the company, so that, should anyone sue, they would be suing Herzstark, not the company, thereby protecting themselves at Herzstark's expense. This ploy now backfired: without the patent rights, they could manufacture nothing. Herzstark was able to negotiate a new agreement, and money continued to flow to him.

Curtas were considered the best portable calculators available until they were displaced by electronic calculators in the 1970s.

An estimated 140,000 Curta calculators were made (80,000 Type I and 60,000 Type II). According to Curt Herzstark, the last Curta was produced in 1972.

The machines have a high curiosity value; in 2016 they sold for around US$1,000, but buyers paid as much as US$1,900 for models in pristine condition with notable serial numbers.

Uses

The Curta was popular among contestants in sports car rallies during the 1960s, 1970s and into the 1980s. Even after the introduction of the electronic calculator for other purposes, they were used in time-speed-distance (TSD) rallies to aid in computation of times to checkpoints, distances off-course and so on, since the early electronic calculators did not fare well with the bounces and jolts of rallying.

thumb|The Curta collection of the Swiss entrepreneur Peter Regenass on display at the Enter Museum Solothurn

The Curta plays a role in William Gibson's Pattern Recognition (2003) as a piece of historic computing machinery as well as a crucial "trade" item.

In 2016 a Curta was designed by Marcus Wu that could be produced on a 3D printer. The Curta's fine tolerances were beyond the ability of printer technology of 2017 to produce to scale, so the printed Curta was about the size of a coffee can and weighed about three pounds.

Further reading

References

  • Curta I Vintage Calculators Web Museum: Mechanical Calculators
  • Curta.org
  • The CURTA Calculator Page
  • Video on internal workings of the Curta by MechanicalComputing
  • Home of www.curtamania.com Many resources
  • http://www.curta.ch Information about Curta / Video about the assembly of a Curta / Book about Curt Herzstark (Kein Geschenk für den Führer - Schicksal eines begnadeten Erfinders)
  • curta.li: model history, user and service manuals, parts photos, blueprints, etc.
  • YACS-Yet Another Curta Simulator. A 3D Simulator in VRML
  • Type and Age of your Curta
  • Files to 3D print a 3:1 scale model of a Curta
  • Curta.fr Mainly focused on maintenance, repair and support. In French.