Microsoft Office Tutorials and References
In Depth Information
Chapter 8: Components That Show Trending
Figure 8-2: You can use area charts to trend over a long time span.
Figure 8-3 demonstrates how a combination chart can more easily call attention to the exact months
when 2010 sales fell below 2009. A combination of line and column charts is a very effective way to
show the difference in units sold between two time periods. We show you how to create this type of
chart later in this chapter.
Figure 8-3: Using columns and lines emphasizes the trending differences between two time periods.
Starting the vertical scale at zero
The vertical axis on trending charts should almost always start at zero. The reason we say almost is
because you may have trending data that contains negative values or fractions. In those situations,
it’s generally best to keep Excel’s default scaling. However, in situations where there are only
nonnegative integers, ensure that your vertical axis starts at zero.
The reason is that the vertical scale of a chart can have a significant impact on the representation of a
trend. For instance, the two charts shown in Figure 8-4 contain the same data. The only difference is
that in the top chart, we did nothing to fix the vertical scale assigned by Excel (it starts at 96), but in
the bottom chart, we fixed the scale to start at zero.
Now, you may think the top chart is more accurate because it shows the ups and downs of the trend.
However, if you look at the numbers closely, you see that the units represented went from 100 to
107 in 12 months. That’s not exactly a material change, and it certainly doesn’t warrant such a
dramatic chart. Actually, the trend is relatively flat, yet the top chart makes it look as though the
trend is way up.
The bottom chart more accurately reflects the true nature of the trend. We achieved this effect by
locking the Minimum value on the vertical axis to zero.