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The addition with a "crosses de Troncet" adder

The input of 4 :

The input of 4 is done by setting the stylus in the hole facing the "4" and pulling down to the end of the slide. 4 is shown in the display.

Adding 3 to the result :

As above, the stylus is engaged in the hole facing the "3" and pulled down to the end of the slide. 7 is now in the display windows.

Adding 6 to the result (how the slide cogged bars work) :

Each time the operator adds a figure, the sliding bar goes down until it blocks against the bottom of the machine. For this reason, in our example, it is mechanically not possible to add 6 to the preceding result. Indeed, the toothed rack can go down only from three units.

glissière Troncet

The solution consists in adding ten and withdrawing 4 units.
The "crosses de Troncet are helpful to do that. When the operator sees the red color at the place where he sets the stylus, this means that the sliding direction must be upward.
In the present example, the operator puts the stylus at "6" in the slide, goes up to the top (4 is subtracted to the units) and takes the turn around the bend (10 is added). The result 13 (6 + 7) appears in the display.