Crystal report summary field on group field

[willemp]

i have a report with a 3 groups in it

A - project
B - person

each record in the report consists of a single realised workday on a
single project by a single person.

so i have records that contain projectname,personname,date,worked
hours, and the hours that where planned for this person on this project
(in total, not specific for this day), month ( this is the month in
which these hours where planned)

in the report i only have to show the total number of realised hours on
a single project per person, but i need all the realisation records
because i need to be able to filter on these.

now the problem is that the planned hours are summerized per
realisation record. And this is obviously not what i want. In order to
work around this problem i have made the third group C - month.
Now i get the single planned months as records in my report. My
question is how to summerize these group records? because any summerize
or total on the planned hours is of all records and never only the
showing group records.