* Translation by Andries de Man

The tens-carry mechanism is an important issue in the history of mechanical calculators. It is not a simple task to convert a primitive curiosity to a useful and sellable product. Usually this is a process of trial and error.

Thomas' arithmometer did not escape from this rule!

I) Thomas' Theorem


To summarize the tens-carry principle used by Thomas, and its evolution, one could very well state:

« A, acting on B, will move C,

that will engage with D and transfer one unit to the next decimal place.

At the end of the cycle, X will let C return to its initial position ».

Explication :

Part A is mounted below the result dial. It could be a peg (1820), a wedge (1850-52), a square block (1856-...) or a tooth (circa 1900-...).
Its shape reveals the tens-carry mechanism used by Thomas de Colmar in his arithmometers, and the large number of improvements he made. You can examine this evolution by clicking the chronological links at the top of this page: each system is described and pictured.

A
1850-52	1856-1900	1900-1907

When passing through ten, A acts on a shaft, a ratchet or a lever (B) and forces a tooth (or gear) C to move. By 1856 a reliable mechanism was constructed. The use of a lever made it possible to limit the number of springs, improving the reliability of the machine. In addition, the lever is pushed horizontally or oblique. This has great advantages: still enabling the escapement of A during its rotation, the horizontal push solves a severe problem that was observed in the 1850 and 1852 model: the lifting of the carriage!
In the 1850 and 1852 models, the force on each lever/ratchet was vertical and tended to cause an inadvertent lift of the sliding part containing the dials (the carriage). As a result, the gears failed to engage and the result would be wrong!

Let's return to our topic!

During its displacement, the tooth (or gear) C will be placed under gear (or tooth) D and engage with it. This will transfer one unit to the next decimal place, that is, the result dial to the left. For the majority of the models build between 1850 and 1907, it was a tooth C that was placed under the gear D. Only the patent of 1880 describes the opposite procedure, but we have never found a machine that corresponds to that patent! Probably a ghost patent....

At the end of the rotation, all elements return to their initial state by the action of a spring or a helical guide.

Summary