Here's the problem: You are writing an SSRS report and you want to sum a value that is in a group header. In Crystal we would do this using a running total field. (sigh)
In the image below, we're written a SOP report and we want to sum the DOCAMNT field. If we just do that, we get a number that is way too big, because it sums for each line in the order. The SSRS way to fix this is to use variables; but that approach is so inelegant.
What we really want is in the DOCAMNT2 column:
Here's a technique that makes this very simple