Do you want to show accumulative average or an average per each group?

If the later, then
Create 4 variables grpWeight and grpValue (initial 0, calculation - sum of the appropriate values, reset at group)

totWeight and totValue (same, but reset at the end of the report).

Then in the group footer you would have
grpWeight/grpValue

and at the report footer you would have
totWeight/totValue

>I have this problem with totals
>
>In a report with a kind of structure like this :
>
>group 1
>group 2
> month1 month2 month3 month4 . . . . . month12
>
>weight
>Value
>----------------
>group2 footer
>
>tot weight
>tot value
>-------------
>group 1 footer
>
>well, i can have the totals weight and value using the "calculate" function of reports, but i dont' know how to get the middle price sum(weight) / sum(value)
>
>How can i do ?