TM 5-6640-212-14
(2) With the repeat key depressed, set 20.125 on
i. Adding and Subtracting Decimals. To preset the
the keyboard (20 to the left of the keyboard decimal
decimals for a group of problems involving addition and
marker and .125 to the right).
subtraction, examine the numbers in all the problems
(3) With the carriage in position 1, turn the
and determine which has the largest number of decimal
operating crank five turns forward. Shift the carriage one
places.
Set the keyboard decimal marker to
place to the right. Make two forward turns. Shift the
accommodate this number of decimal places. Set the
carriage to the right. Make four forward turns.
lower dial decimal at the same number. The upper dial
decimal is a zero (0). For example, to add 12.25 to 3.333
(4) The result (answer) on the lower dials should be
or to subtract 75.242 from 160.0:
8.553125. Not that the .425 appears in the upper dial to
the right of the decimal marker and the lower dials
(1) Set upper dial decimal setting to 0 and
decimal marker correctly points off the answer.
keyboard and lower dial to 3 because three is the
(5) Always set the decimal for a whole group of
greatest number of decimal places that appears in these
problems to avoid changing the decimal markers for
figures.
every problem. To do this for a group of multiplication
(2) Set the numbers on the keyboard exactly as
problems, simply find the largest number of decimal
they are written. The figures that appear to the left of the
places appearing in the numbers to be set on the
decimal point should be set to the left of the keyboard
keyboard. Set the keyboard decimal marker for this
decimal marker, and those that appear to the right of the
number. Find the largest number of decimal places to
decimal should be set to the right of the keyboard
be entered in the upper dials. Set the upper dial decimal
decimal marker.
for this number. Set the lower dials decimal at the sum
(3) Follow the instructions for addition and
of these two. Enter all figures around these preset
subtraction given in d (1) and (2) above, and the result
decimals and the results will be all correct. The following
will always be correct.
example illustrates this:
j. Multiplying Decimals. To multiply, set the larger
24.75 x .35 = 8,6625
number on the keyboard and, with the operating crank,
32.5 x .24 = 7.8
turn the other number into the upper dials. When this is
110.333 x 1.4 = 154.4662
done, the answer appears in the lower dials. Therefore,
The largest number of decimal places in the numbers
when multiplying decimal numbers, set the keyboard
which go on the keyboard is three; in the numbers which
decimal marker to accommodate the largest number in
go in the upper dials, two. Therefore, the decimal setting
the problem and the upper dials decimal marker to
should be:
accommodate the other number. Then, following the
Upper dials
2
rule for decimals (h above), add the number of decimal
Keyboard 3 Lower dials
5
places on the keyboard to the number of decimal places
k. Dividing Decimals. In division, as explained in the
in the upper dials and set the lower dials decimal marker
instructions for simple division, both numbers (divided
at this number of decimal places. This is exactly how
and divisor), are set on the keyboard. Therefore, when
you point off the decimal when multiplying by pencil and
working with decimal numbers, examine all numbers to
paper; add the number of decimal places in the two
find the largest number of decimal places appearing in
numbers and point off this many places in the result. All
the whole group of problems at hand. Set the keyboard
decimal markers should be set before beginning any of
decimal at this number. To set the upper dials decimal
the work. For example, to multiply 20.125 by .425:
always decide how many decimal places are required in
(1) Set the larger number (20.125) on the
the answer and set the decimal marker to one more
keyboard. It has three decimal places so the keyboard
place than this (to permit rounding off). Again, for the
decimal marker should be set at three. Set the other
lower dials decimal, add the keyboard and upper dials
number (.425) in the upper dial, setting the upper dials
decimal and set the lower dials decimal at this number.
decimal at three. Add the two (3 + 3 = 6) and set the
lower dials decimal at six. Set the decimal markers
accordingly and do the above example following the step
by step instructions below.
2-56
