HP Intelligent Management Center Standard Software Platform - Manual (Page 271)

Note:
This formula prints the same value that @RunningTotal prints as the
running total for the last record in each group. But since 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.
Crystal Reports 2008 SP3 User's Guide 271
11 Running Totals
Creating running totals using a formula