How do I put a running total in a Reports 6i Report?

Question

I need to write a report which shows a running total at the foot of each page. The report is a series of (potentially) multi-page sections each formatted like this:
Page 1
======
Tom £100
Dick £150
Harry £100
Sub Total £350
Page 2
======
Peter £200
Paul £50
Mary £100
Total £700
Lines are of variable height, so I can't predict how many there'll be on a page.
The help system just tells me to "use a summary field". Yeah, right. Can anybody give me some more detailed instructions?
-- Chris Hunt

Answer 1

Thanks for that.
I didn't really express the problem as well as I might have done, as the Sub-Total needs to be the sum of all the items on the current page and on all preceeding pages. resetting on page just gives you the total for that page.
I did find a way to do it. First you set up a summary field in the same group as the data lines, summing the amount and resetting on the parent group. This gives you a running total for each row:
Page 1
======
Tom £100 £100
Dick £150 £250
Harry £100 £350
Page 2
======
Peter £200 £550
Paul £50 £600
Mary £100 £700
You don't actually output this summary field in the prinout (except when debugging :-) ). Now create a summary field at the foot of the page, or in the margin. Set its value to the Max() of the running total summary, resetting on page. That gives you the amount required, assuming all individual amounts are positive.
If it's possible to have negative amounts, I expect that using Last() instead of Max() for the page summary would do the trick.