About Accumulator expression functions
Using the Edit Expression Binding form, you can use the accumulator expression function to calculate and show sub-totals and totals on form reports without examining the entire data set to calculate each total.
Accumulator functions only work on report forms and can be used in detailed regions of a report to show running totals.
In form reports, Page accumulator functions can be used to calculate and display accumulated values by page. The page-based accumulators are used in a page-based report format such as PDF,and if used in a non-paged format such as Excel single worksheet, the values accumulate throughout the entire report.