number of students in training, broken into three groups: total in
training, total in OJT, and total in formal school.
Figure 127. Three variable curve chart
(3) Step curve chart (figure 128): When the data has abrupt
changes, you would use this type of curve chart to present it. However,
there are two disadvantages to using this type of chart. The abrupt
change in the line causes it to lose the trend or feeling of movement
through time. The second disadvantage is when plotting two or more
lines on the same chart, they may cross or fall on the same vertical or
horizontal grid. This often confuses the reader and the chart loses its
effectiveness. When using this Chart to present data, you must ensure
that the reader can readily understand and evaluate the data the chart
presents.
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