The comptometer is a type of mechanical calculator, in use before electronic machines were invented in the 1960s and '70s. This model was made by the Felt & Tarrant Manufacturing Company of Chicago and looks like a model from the 1940s. 

They were incredibly fast for addition as the operator could use all fingers to strike the keys simultaneously, sometimes making them superior to calculators. Complicated, they required hours and hours of training to use.


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