Rotary calculators

These mechanical calculators do not print: instead the results are displayed on a series of rotating number dials. Their main advantages compared to printing calculators are their greater speed, particularly in division, greater capacity and greater flexibility for complicated calculations.

Most of the internal mechanisms are evolutions of machines developed in the 1930's and 40's. The last of the rotary calculators attempted to incorporate advanced features such as shortcut multiplication, automatic decimal point placement and mechanical memory. However, as the cost of electronic calculators dropped, even the most advanced mechanical models were not competitive, and the rotary calculator was gone from the market by 1970.