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Harts Mercantile Calculating Machine
Harts Adding Machine

Wanted: Hart's Mercantile Computing Machine

Hart's Mercantile Computing Machine, also known as a Hart's Calculating Machine, was patent 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 device was constructed of pressed brass. Hart's calculator was capable of addition, subtraction, multiplication and addition.

There were 2 version produced of the Hart's. One with a knob mounted to the rear of the brass discs and another mounted to a paddle, like the Hatfield Adder. Both version originally included a stylus which, unfortunately, surviving examples are often missing.

Have one for sale? Please email me at or call +1 860 727 2252

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