Background:
I am a beginner crystal report user and I am trying to design a cross-tab report with sales data from our opportunity pipeline.  The rows consist of opportunity stage grouped by week and the columns consist of the opportunity segment.

Problem:
I have the basic design layout out in crystal reports, now I need to include some calculations like the 'difference' and 'percent change' in a certain area, preferably at the bottom of the report.  How do I insert the calculation to the bottom of the page (instead of inline below the calculated member)?  In addition, I would like to filter 'This Week' and 'Last Week' to do a week-on-week comparison.  How do I dynamically filter this week vs last week with a calculation?

Any direction or solutions would be greatly appreciated.  Thanks in advance!

FYI, here is an Insertion Formula: GetRowGroupIndexOf(CurrentRowIndex) = 2 and GridRowColumnValue("Opportunity_Snapshot__c.CreatedDate") = CDateTime (2010, 08, 21, 03, 00, 00) and GridRowColumnValue("Opportunity_Snapshot__c.Stage__c") = "Lead"

Does the insertion formula have anything to do with where the calculation is placed on the layout or is the insertion formula just where the calculation references the members?

Here is an example of the desired result: