On 12th April, 1859, Caroline Winter presented the patent model of her “Improved Adding Machine”. Winter, who came from Miami County, Ohio, and ran a general store in Piqua, invented a simple single column key adding machine which only needed a minimal amount of components and above all else stood out due to its secure and straightforward operation. Her use of an elementary switching latch mechanism is characteristic, since this mechanism had only been used in very few calculating machines before, for example those made by Jean-Baptiste Schwilgué. Winter’s adding machine is designed in a clear and self-explanatory way and is mostly made of wood, except for the gear wheels. The machine can calculate with numbers up to 600 and shows its result with two indicators. The bigger one of the two gauges displays numbers 1 to 100. The indicator of the smaller gauge for the hundreds moves continuously and shows the numbers from 1 to 6. A stopping mechanism on the inside of the machine causes the machine to display 600 as its highest number instead of 699. When the highest number has been reached, the machine can be reset to its starting position by the use of a clearing lever.