Fred's mechanical calculators . Highlights and list .

Was constructed by the firm of Theo Müggli in Zurich (Switzerland) starting in1923 . It's working principle makes it stand apart from practically all other contemporary machines : back and forth rocking toothed segments that make intermittent contact with the counters . Mechanically it only could perform additions ( and multiplications) , so substractions (and divisions) had to be made by means of complementary digits . Being cheaper than other machines was its main (and perhaps only) selling argument .

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