In 1867, Amos Mendenhall of Cerro Gordo, Indiana, patented a practical calculator (US patent 67786). The patent model of the device (up to 1880, the US Patent Office required inventors to submit a model with their patent application) is still preserved in the National Museum of American History, Washington, D.C. (see the image below).
The practical calculator of Amos Mendenhall is a square metal box with overall measurements: 5.4 cm x 13 cm x 13.8 cm. The box has a boss in the centre inside, in which the shaft of a cylinder is to turn.
The headstone of Amos Mendenhall in Buena Vista Cemetery, Winchester, Indiana (he shares a headstone with his niece, Leila Bell Mendenhall, who died only two days prior)