uch figure disks be placed side by side, their windows lying in a row,
then any number of six places can be made to appear, for instance 000373.
In order to add 6425 to this number, the disks, counting from right to
left, have to be turned 5, 2, 4 and 6 steps respectively. If this is done
the sum 006798 will appear. In case the sum of the two figures at any disk
is greater than 9, if for instance the last figure to be added is 8 instead
of 5, the sum for this disk is 11 and the 1 only will appear. Hence an
arrangement for "carrying" has to be introduced. This may be done as
follows. The axis of a figure disk contains a wheel with ten teeth. Each
figure disk has, besides, one long tooth which when its 0 passes the window
turns the next wheel to the left, one tooth forward, and hence the figure
disk one step. The actual mechanism is not quite so simple, because the
long teeth as described would gear also into the wheel to the right, and
besides would interfere with each other. They must therefore be replaced by
a somewhat more complicated arrangement, which has been done in various
ways not necessary to describe more fully. On the way in which this is
done, however, depends to a great extent the durability and trustworthiness
of any arithmometer; in fact, it is often its weakest point. If to the
series of figure disks arrangements are added for turning each disk through
a required number of steps, [v.04 p.0973] we have an addition machine,
essentially of Pascal's type. In it each disk had to be turned by hand.
This operation has been simplified in various ways by mechanical means. For
pure addition machines key-boards have been added, say for each disk nine
keys marked 1 to 9. On pressing the key marked 6 the disk turns six steps
and so on. These have been introduced by Stettner (1882), Max Mayer (1887),
and in the comptometer by Dorr Z. Felt of Chicago. In the comptograph by
Felt and also in "Burrough's Registering Accountant" the result is printed.

These machines can be used for multiplication, as repeated addition, but
the process is laborious, depending for rapid execution [Sidenote: MODIFIED
ADDITION MACHINES.] essentially on the skill of the operator.[1] To adapt
an addition machine, as described, to rapid multiplication the turnings of
the separate figure disks are replaced by one motion, commonly the turning
of a handle. As, however, the different disks have to be turned through
different steps, a contrivance has to