Place this formula in the Group
Footer #1 section of your report.
Because the Group Footer #1 section appears
once for every group, @AmountDisplay will execute each time a group ends. So,
the value stored in the Amount variable will be printed each time the group
changes.
Note: This formula prints the same
value that @RunningTotal prints as the running total for the last record in
each group. Because it is printing it in the Group Footer section, it acts as a
group subtotal, not as a running total.
On your report, each row in the running total
column displays the current record value added to the previous values. The
running total starts fresh with each new group, and the final running total for
each group becomes the subtotal for that group.