b. Curve or Line Charts.
This chart provides a way to present
cumulative or noncumulative events that occur over a period of time (time
series). Since the person viewing the chart can readily follow a line,
the line creates the impression of moving through time and magnitude with
For example, you could use this type of chart to show the
number of hours spent performing operator maintenance each month. You
can design a line chart to show more than one variable, an average, or
desired rate line.
When designing a curve or line chart, use the same process you used for a
column chart when selecting the scale, title, and chart construction. A
completed curve or line chart presents a grid system for plotting the
data with the vertical and horizontal line drawn.
When plotting data on a curve or line chart, you plot single points only.
The point is the intersection of the data and scale lines when you
connect the points using the method desired for the chart. After you
have plotted and connected the points, you ink and letter the chart using
the same process used for a column chart.
There are several types of curve or line charts: broken curve, smooth
curve, and step curve.
(1) Broken curve or line chart.
This type of chart presents
noncumulative quantities at a given time. This means the values plotted
represent the total at a specific time.
Even though a straight line
connects the points on the chart, you cannot assign any intermediate
values from this line. The line shows direction or trend, and it does
not assign any values. When using this type of chart, you must take the
data from the same day each month. Otherwise, the chart will not present
an accurate picture of the totals.
For example, figure 1-24 shows a broken curve chart that presents data
showing that 50 people graduated from the on-the-job training program in
July, and 60 people graduated from the on-the-job training program in
August. Someplace between the plotted points for the two months the line
crosses the 55 quantity line.
However, that does not mean you can
conclude that at that point in time 55 people graduated from the program.
(2) Cumulative (smooth) curve or line chart. When using this type
of chart to present data, the reader can assign intermediate values from
the running, smooth curve. This type of curve or line is an effective
way of presenting the growth or decline of an activity. When you use
this chart with a projected curve or line, plotting the actual data shows