Crystal Reports for Rational Application Developer Designer Guide

To display a total that evaluates each record and provides a running sum of all the values in a field (or all the values in a certain set of values), a running total field needs to be created and placed in the report. If the first three values in a field were 2, 4, and 6, a running total would print 2, and then 6 (the sum of 2 + 4), and then 12 (the sum of 2 + 4 + 6).