Roth Adding Machine
This two-place adding machine designed by Didier Roth (1800-1885) is very well suited for demonstrating how a tens-carry mechanism functions. At a time when the tens-carry mechanism often limited the number of places of a machine, Didier Roth had a cardinal idea. He designed a tens-carry mechanism that stored the necessary force in a first step, where it remained until it was needed. This he achieved by using a disc consisting of two curved segments placed off-center. When turned, this disc presses the tens-carry lever – spring-loaded towards the axle – increasingly far away from this axle, in accordance with entered number. When the result mechanism shows 9, then the furthest point has been reached and the spring is stretched maximally. When going from 9 to 0, the tens-carry lever slips over an edge of the segmented disc and is returned to its original position by the spring. At the same time the other end of the tens-carry lever turns the wheel of the next higher place one position on. This mechanism can function over many places without a problem. The setting mechanism shows that every cogwheel of the calculator has twice as many cogs as there are places in the setting mechanism, as half their circumference deals with the digits 0 to 9. Hence there are also two segmented discs per place. Roth built only a small number of these machines himself; later Wertheimber patented it and built and sold it outside France. Most of the original machines are today in the Musée des Arts et Métiers in Paris. Further models are to be found in numerous technical collections world-wide. The Arithmeum has an eight-place machine (FDM 7341) dating from 1843 and also a counting machine built by Wertheimber (FDM 6096).