COGNOS: Difference between Two values in a COLUMN

Suppose I have report output as follows…

Now, I want to find difference between 2006’s Revenue and 2007’s Revenue in its footer…
To Resolve this follow the steps
1)      Create a list report as follows

2)      Create a Filter to only show 2006 and 2007 as follows


3)      Create “list overall” footer as follows..

4)      Select the summary row (The overall footer ) and split it
5)      Unlock the report
6)      Drag query calculation to the Cell as follows..

7)      Give any name and enter the following expression in Expression definition box..

8)      Click OK and Run the report, you will get output as follows..