In the body of the report,
right-click the {CUSTOMER.LAST_YEARS_SALES} field and select
Summarize.
The summary is inserted in the Group
Footer.
If you look at the subtotals for each
group, you will notice they are inaccurate. This is because the
{CUSTOMER.LAST_YEARS_SALES} field is duplicated for each order in the report.
Follow the rest of this procedure to see how a running total produces an
accurate result.