1.  Create a new Constituent Query
2.  On the Criteria tab, select:
Gift date equals [the first time period on the Comparative Report]
3.  Save and Close the Query.
4.  Create a New Comparative Report.
5.  For period one, ensure this is the same date range included in the query.
6.  From the Format tab, select Detail and mark Increase as the Variance to Include.
7.  Preview the Report.