Generate Auto Serial No.

[haidervb]

Hello.
I have a report of multiple groups.
and i want to generate a serial no. based on first group.the serial number remain 1 unless first group be ended.
I insert 'Group Number' option but it also count other groups.
group fileds are following.

machine category (First Group)
department (sencond group)
because a category lies on different departments, so i concentrate on machine category.
please solve this problem.

Thanks
Haider.