Crystal Reports summing within a sub group

In Crystal Reports XI, I'm trying to sum within a sub group, I've grouped by two fields.

Is normally sum by doing something like:

Sum({@Formula_Field},{Group_1_field}) 

But I've realised this returns all of the formula field within the first grouping. I was wondering if there was a way to sum only then values within the subgroup of group 2 within each of the group 1 groups. I need to have a calculated value that is it's own field for each subgroup which is the same for each line of the subgroup once calculated.

    Column_1  Column_2  Column_3 
Grouping_1
    Grouping_2
Row_1 10        20       30
Row_2 10        10       10
    Grouping_2
Row_3 5         5        5
Grouping_1
    Grouping_2
Row_4 8         8        9
Grouping_1
    Grouping_2
Row_5 6        7         6

Using my formula above for the first grouping it return depending on which column was your formula field:

Ideally I want to know how to sum only the rows in the second grouping something like:

Sum({@Formula_Field},({Group_1_field}&{Group_2_field})) 

Although I know that code is nonsense just to hopefully illustrate what I'm trying to achieve, the outcome when it works would give:

The difference being between row 1/2 & 3 where there is a different subgroup between the rows meaning the summing happens across only the first two rows and then separately for row 3 the new sub group.

Thank you for any advice!

// Place this in Details (or Group 2 sections if you prefer)
Sum({@Formula_Field}, {Group_2_field})

This will give you the same value on each row within the current Group 2

Row  Column_1  Column_2  Column_3
1    20        30        40
2    20        30        40
3    5         5         5
4    8         8         9
5    6         7         6

You have to keep in mind that {Group_2_field} is the actual field you used to define Group 2 (not a formula unless the group was created on that formula). If {@Formula_Field} itself depends on print-time values, this still works, but if you see evaluation-order issues, see below:

Reset the subgroup sum in Group2 Header by creating a formula called @SubSum_Reset and place it in Group 2 Header:

WhilePrintingRecords;
Global NumberVar SubSum := 0;

Create a formula as@SubSum_Add and place it in Details:

WhilePrintingRecords;
Global NumberVar SubSum;
SubSum := SubSum + {@Formula_Field};

Create a formula called @SubSum_Finalize and place it in Group 2 Footer:

WhilePrintingRecords;
Global NumberVar SubSum;
Global NumberVar SubSumFinal := SubSum;

Finally you can get that in @Subgroup_Total_Display and place it in Details where you need the repeated value

WhilePrintingRecords;
Global NumberVar SubSumFinal;
SubSumFinal;

This should resolve your issue as it guarantees the same (final) total on every line of the subgroup, even for print-time formulas.

Hope it helps