Hart's Mercantile Computing Machine,  also known as Hart's Calculating Machine, was patented in 1878 by William Hart of Kirksville, MO. It was produced by the Scovill Manufacturing Co. of Waterbury, CT. Waterbury, to this day, is known as "Brass City" so it is fitting that the device was constructed there of pressed brass. With its 3 concentric brass discs, the Hart's calculator was capable of addition, subtraction, multiplication and addition up to 9,999.

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