What happens when you use the same scale to compare values that are actually in different scales?

Have a look at this chart that was generated using Reporting Services and notice that you can barely see the gold columns for the Average Sales values.

The data (see the table next to the chart) tells us that a scale ranging from 0 to 625,000 is needed to plot the Total Sales, while a scale ranging from 0 to only 10,000 would do for the Average Sales. Though Average Sales and Total Sales are on different scales, the chart plots them on one axis, leading to the tiny columns for Average Sales.

Learning Point: When a series in a chart is not measured on the same scale used for the other series in the chart, a secondary axis can make the chart easier to read.

Let’s put in a secondary axis for the Average Sales.

1. In the report designer, right-click the data series on the graph (in our case, that will be the gold column in our column chart) and select Series Properties…
   
2. Select Axes and Chart Area, then Secondary for either vertical or horizontal axes as needed (in our case, we will select Secondary under Vertical axis), and then click OK when done.
   
3. Now when we preview the report, it’s a lot easier to see the Average Sales.
   
   Even though this gives us a clearer picture of the variations in the Average Sales, it’s a bit odd to see the gold columns side-by-side with the blue columns; it still looks a lot like they are on the same scale.Learning Point: When comparing series on different scales, using a different graphic representation for each series makes the chart clearer.
   Let’s change the gold column to a line.
4. In the report designer, right-click the data series on the graph (in our case, that will be the gold column in our column chart) and select Change Chart Type…
   
5. Select a new chart type for the series and then click OK when done; in our case, we’ll select the first line chart type.
   
6. The chart looks much better now. It still shows us what the Average Sales does through the different Quarters together with what the Total Sales does, but with the different chart types, they don’t look so tied together anymore. It’s easier to see that they are on different scales.
   
   …and we can even make the gold line a bit thicker.
7. In the report designer, right-click the line and select Series Properties…
   
8. Select Border, then change the line width as desired, and then click OK when done; in our case, we’ll change the line width to 2.5.
   
9. Much better!
   

Enjoy!
Peter Avila
SQL Server Instructor – Interface Technical Training
Phoenix, AZ