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.

The chart

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

||content||

to,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