Microsoft Office Tutorials and References
In Depth Information
Pie Charts Make Horrible Time Comparisons
However, if the spacing of events along the time axis is haphazard, you definitely want to
make sure that Excel uses a date-based axis.
Accurately Representing Data Using a Time-Based Axis
Figure 3.6 shows the spot price for a certain component used in your manufacturing plant. To find this data, you
downloaded past purchase orders for that product. Your company doesn’t purchase the component on the same day every
month; therefore, you have an incomplete dataset. In the middle of the dataset, a strike closed one of the vendors,
spiking the prices from the other vendors. Your purchasing department had stocked up before the strike, which allowed your
company to slow its purchasing dramatically during the strike.
The top chart uses a
textbased horizontal axis:
Every event is plotted an
equal distance from the
next event. This leads to
the shaded period being
In the top chart in Figure 3.6, the horizontal axis is set to a text-based axis, and every data point is plotted an equal
distance apart. Because your purchasing department made only two purchases during the strike, it appears the time
affected by the strike is very narrow. The bottom chart uses a date-based axis. In this axis, you can see that the strike
actually lasted for half of 2010.
To learn how to highlight a portion of a chart as shown in Figure 3.6, see “Highlighting a Section of
Chart by Adding a Second Series,” later in this chapter.
Usually, if your data contains dates, Excel defaults to a date-based axis. However, you
should always check to make sure Excel is using the correct type of axis. A number of