I understand that the Curta calculator was invented by Curt Herzstark. Much of the work done while he was a prisoner of the Nazis during WW2. Although he had begun work on the design prior to the outbreak of WW2 an had filed a few patents. he was imprisoned before he could finish it. he continued working on the design while in prison with the full knowledge of the SS.
After the war he completed the design and bang production around 1947. Some 200,000 were produced over they next 20 or so years. when electronic calculators pushed the curt out of the market.
They are still highly prized by collectors, and bring high prices.
Good luck to you guys who try to make one, I understand they are a nightmare to assemble.