at the lower left-hand corner of the chart. You use the horizontal lines
for the scale and the vertical and horizontal lines for plotting the data
on the chart.
When selecting the scale for a chart, you must consider the range of
values the chart presents.
Usually, the lowest line on the chart
represents zero; therefore, the height of the finished chart depends on
the range of values presented. The larger the range of the values, the
taller the finished chart.
Other factors you must consider when
selecting the proper scale is that all well-constructed charts (except
percentage surface charts) have a space between the largest value plotted
and the top of the chart.
Also, research has proven that people comprehend and retain even numbers
quicker than odd numbers while reading. Therefore, using even numbers in
the scale increases the effectiveness.
To illustrate the selection of the correct scale for a chart, consider a
chart that shows the cost of operating Army installations.
shows the operating cost of post A as ,500,000, post B as ,250,000,
and post C as ,000,000.
The actual range of the chart is
,000,000, which includes the additional space at the top of the chart.
Common sense dictates that you cannot design a chart with 4,000,000
horizontal lines, each representing one dollar.
The only logical
alternative you have is to design a compressed scale that fairly
represents each amount on the chart. To find the best interval for the
data you must chart, review the data and find the interval that fairly
represents the values you must plot.
For this chart, 0,000 serves
this purpose. When using 0,000 as the major interval on the scale,
you must have 17 horizontal lines (which includes the zero line):
,000,000 (largest interval) + 250,000 (scale interval) = 16
16 (interval lines) + 1 (zero line) = 17 (lines required)
You have now determined the major interval you want to use on the chart.
You also must determine if the scale fits in the total area you have
allotted for the chart. First, you must take away any top and bottom
borders from the area. Then, divide the remaining height by the number
of spaces required. If the space intervals between the horizontal scale
lines are satisfactory, you can use that scale. For example, you are
using a chart board that measures 15 x 20 inches. Subtract the