sk through one "step" or adds 1 to the figure under the window. The racks
are moved by an arrangement contained in the section to the left of the
slots. There is a vertical plate called the multiplication table block, or
more shortly, the _block_. From it project rows of horizontal rods of
lengths varying from 0 to 9 centimetres. If one of these rows is brought
opposite the row of racks and then pushed forward to the right through 9
cm., each rack will move and add to its figure disk a number of units equal
to the number of centimetres of the rod which operates on it. The block has
a square face divided into a hundred squares. Looking at its face from the
right--_i.e._ from the side where the racks lie--suppose the horizontal
rows of these squares numbered from 0 to 9, beginning at the top, and the
columns numbered similarly, the 0 being to the right; then the
multiplication table for numbers 0 to 9 can be placed on these squares. The
row 7 will therefore contain the numbers 63, 56, ... 7, 0. Instead of these
numbers, each square receives two "rods" perpendicular to the plate, which
may be called the units-rod and the tens-rod. Instead of the number 63 we
have thus a tens-rod 6 cm. and a units-rod 3 cm. long. By aid of a lever H
the block can be raised or lowered so that any row of the block comes to
the level of the racks, the units-rods being opposite the ends of the
racks.

The action of the machine will be understood by considering an example. Let
it be required to form the product 7 times 385. The indices of three
consecutive slots are set to the numbers 3, 8, 5 respectively. Let the
windows gg opposite these slots be called a, b, c. Then to the figures
shown at these windows we have to add 21, 56, 35 respectively. This is the
same thing as adding first the number 165, formed by the units of each
place, and next 2530 corresponding to the tens; or again, as adding first
165, and then moving the carriage one step to the right, and adding 253.
The first is done by moving the block with the units-rods opposite the
racks forward. The racks are then put out of gear, and together with the
block brought back to their normal position; the block is moved sideways to
bring the tens-rods opposite the racks, and again moved forward, adding the
tens, the carriage having also been moved forward as required. This
complicated movement, together with the necessary carrying, is actually
performed by one turn of the handle. During the f