Curta 1

Serial number 16866, June 1952
Accessories Metal box, bottom covered by velvet cloth.
Condition Cosmetically very good.
Mechanically, it has its problems: Zeroing the accumulator and counter dial with the "clearing ring" does not reliably work. Turn the clearing ring slowly gives best results.
Rotating the main handle occasionally jams and leaves the digits in the accumulator in in-between states.
Repairs, Comments
Acquired 12.3.2012
Type, Precision, Input mode Simple, 11 BCD digits, no exponent, fully mechanical
Programmable No
Memory None
Display Various dials on the side and the top of the unit
Special features No batteries required!
Original Pricing, Production According to various sources:
Curta I: October 1948 to November 1970, approx. 80,000 units, serial numbers start at 1, 425 DM (212 Euro) in 1965.
Curta II: January 1954 to November 1970, approx 60,000 units, serial numbers start at 500000, 535 Euro (268 Euro)
Batteries None.
Dimensions Diameter 5.3cm (with clearing lever retracted), Height 8.6cm, 10.6cm including operation handle
Capsule: Height 12cm, diameter 6.2cm
Links by Jan Meyer offers a wealth of information about the Curta. It includes a detailled biography of Curt Herzstark who designed the mechanical masterpiece. with even more information, among them operation instructions.
Curta on Wikipedia.
Curt Herzstark on Wikipedia.
Manual Gebrauchsanweisung für die CURTA (PDF, 30 pages, German, courtesy, May 2003)

Interview with Curt Herzstark, September 1987, Nendeln, Liechtenstein. Conducted by Erwin Tomash, Charles Babbage Institute, The Center for the History of Information Processing, University of Minnesota, Minneapolis.
English version, PDF, 67 pages.
German version, PDF, 86 pages.
Comment I had never seen a real Curta before and was surprised how small it was!
The seller, Yehuda from Israel, writes about his Curta: "I've bought it from MSU professor Harry Oman's estate at 2007. The reasons that I have bought it was two: First because my dad (Jacob 85) has been, as a teenager, at the same concentration camp Buchenwald like Curt Herzstark, and I'm proud that a Jewish person invented this wonderful and genius machine inspite of the condition he was faced with; secondly because I have been many years a senior CAD engineer at Intel (more then 30 years) and I adore this first portable mechanical "computer"."


Obviousely, the traditional performance index doesn't make sense for the mechanical Curta. Nevertheless, lets take a look at how quickly calculations could be solved with a Curta in comparisn with other methods.
PaperMath is known since the old Babylonians who used it maybe even before 2000 BC. Math on paper came with the introduction of papyrus by the Egyptians. And, as we all remember from school days, manual numerical calculations have a nice property: Precision scales nicely with the time invested, it is more or less invers proportional to speed. (Actually, speed is proportional to 1 / precision²). Division is not significantly slower than multiplication.
But in general, math on paper is horribly slow: Multiplying 1.23 by 4.56 takes me about 30 seconds.
Slide RuleSlide rules were known since the 15th century and in 1850 Amadee Mannheim invented the design which was in use until their decline in the 1970s.
Slide rules have one huge advantage: They are fairly fast: Multiplying two numbers only requires to move the inner rule to the desired position and to read off the result from the outer rule - or vice versa. Division is as fast as multiplication. Multiplying or dividing two numbers takes about 15 seconds (depending on how much time is invested to adjust the rules precisely).
But the disadvantage is the poor precision of a slide rule: More than 2-3 digits is simply not possible! Consider: A traditional slide rule is about 30cm long; if a 3-digit precision was desired one has to move the slides accurately to 1/1000th of its length, that is 0.3mm. There is no way to get any better than that.
In other words: With a slide rule the precision does not scale with the time invested.
CurtaMechanical calculating machines were known since the 16th century and built in series in the 17th century. Their decline came with the electronic devices in the 1970s. For most of their time they coexisted with slide rules and it is obvious why: Their advantage was high precision, but that came at the cost of very very low speed.
Multiplying 1.23 by 4.56 takes 30 seconds on my Curta. Dividing is even way slower. Compared to math on paper however, it has the advantage that the speed does not significantly decline with precision. And even better: Human error is largely avoided (although I'm not sure the delicate mechanics always worked flawlessly).
Electronic CalculatorThe first functioning transistors were built in 1947, the first integrated circuit 1958. It took until about 1967 until Texas Instruments built the first more or less pocket sized calculator. In 1970 the first microprocessor, the Intel 4004 was designed, and then in 1972 Hewlett Packard introduced the HP-35 which sounded the death knell for all slide rules and mechanical calculating machines.
Obviousely, electronic calculators combine the benefits of slide rules and mechanical machines: They are both fast and precise. Keying in 1.23 times (or divided by) 4.56 takes around 4 seconds. This is not significantly faster than a slide rule. But the electronic calculator allows for high-precision math (eg integration and root finding) which is simply not possible at all with a slide rule. A mechanical calculating machine could deliver the precision needed for these types of problems but it would be way too slow.
In fact, the time needed for an electronic calculation is really limited by how fast the user can enter the numbers on the keyboard. The calculation itself is more or less instantaneous.
Historical Summary
  • For a few thousand years numerical calculations were only possible on paper or clay. Depending on the problem it could be arbitrarily precise at the cost of speed. In general it was very very slow.
  • In the 16th century two inventions improved the situation: Slide rules made calculations fast but had a very limited precision; calculating machines were precise but still rather slow.
  • In the 1970s both slide rules and calculating machines were obsoleted by electronic devices which delivered instantaneous results with arbitrary precision (at least compared to what was available before).


The workings of a Curta are straight-forward but very clevery designed!
  • The "Operating Handle" may only be turned clockwise.
  • One turn of the Operating handle performs an addition or - if it is pulled out a little bit - a substraction.
  • Turning the "Clearing lever" once resets the "Result Dial" and "Counter Dial" to 0.
  • The small movable knobs can be used to track the decimal point.
Result-dial  += Number-entry * 10^Power-of-10

Counter-dial +=            1 * 10^Power-of-10
SubstractionResult-dial  -= Number-entry * 10^Power-of-10

Counter-dial -=            1 * 10^Power-of-10
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