"Willgodt Theophil Odhner (in Cyrillic, Вильгодт Теофил Однер) was a Swedish engineer and entrepreneur, working in St. Petersburg, Russia. He was the inventor of the Odhner ...
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Arithmometer, which by the 1940s was one of the most popular type of portable mechanical calculator in the world.
According to a brochure distributed by Odhner's company at the Paris World exposition of 1900 "...Odhner had, in 1871, an opportunity to repair a Thomas calculating machine and then became convinced that it is possible to solve the problem of mechanical calculation by a simpler and more appropriate way". It took him 19 years to perfect the design of this new machine so it could be manufactured effectively." - (en.wikipedia.org 23.12.2020)