On 29 September 1863, one Milton C. Jeffers of New York was granted a patent (US patent No. 40105) for simple adding device, quite similar to the earlier calculating devices of his compatriots Jabez Burns and John Ballou. In Jeffers’ patent is mentioned, that his device is an improvement of the machine of Joseph Harris from 1861 (US patent 31016).
We know almost nothing about the inventor. Milton Clifford Jeffers was born around 1823 and died on 26 October 1896. He used to work as a patent agent and broker, and is an assignee and assignor of quite a few machinery patents in USA and Canada in different areas, let’s mention only: fodder-cutter and corn-husker (US patent No. 74370 from 1868), corn husker (US patent No. 108484 from 1870), panoramic school apparatus (US patent No. 120072 from 1871), attachment for railway cars (US patent No. 234265), and ship ventilator and fog alarm (Canadian patent No. CA6356A).
The patent model of the device (see the lower photo) survived to our time and is kept now in the collection of National Museum of American History in Washington, D.C.
The adding machine of Jeffers is a brass, steel and paper device with overall measurements: 10 cm x 11.5 cm x 10 cm.
This simple machine is a lever-set adding device, featuring a frame of two brown round end pieces joined by a central shaft and by two handles of brass at the outside. The shaft carries six toothed wheels that may be rotated with the fingers. Each wheel has 30 teeth and is joined to a brass ring on its right (thus implementing a carry mechanism). Around the rim of each ring is a slip of paper with the digits from 0 to 9 printed on it three times. One third of each ring is covered by a metal piece with a window at the bottom and the digits from 1 to 9 engraved on it.
To enter digits, the operator must rotate wheels forward the distance indicated by these digits. The total appears in the windows.
The carrying processes are being performed by means of the inclined plate attached to the casing, as described in the patent of Joseph Harris.