How to do it...

To implement this recipe, do the following:

1. Create the following measure:

AcrossThenDown = 
    VAR __Table = ALL('R06_Table')
    VAR __ColA = MAX('R06_Table'[Col A])
    VAR __ColB = MAX('R06_Table'[Col B])
    VAR __Count = COUNTX(FILTER(__Table,[Col A] < __ColA),[Col A]) + 1
    VAR __PreviousRows = 
        SUMX(
            FILTER(__Table,[Col A]<__ColA),
            [Value]
        )
    VAR __CurrentRow = 
        SUMX(
            FILTER(__Table,[Col A]=__ColA && [Col B]<=__ColB),
            [Value]
        )
RETURN
    IF(ISINSCOPE('R06_Table'[Col A]),
        IF(__Count = 1,
            __CurrentRow,
            __PreviousRows + __CurrentRow
        ),
        IF(ISINSCOPE('R06_Table'[Col B]),
            SUMX(
                FILTER(__Table,[Col B] <= __ColB),
                [Value]
            ),
            SUMX(__Table,[Value])
        )
    )

2. On a Report page, create a Matrix visualization.
3. In the Matrix visualization, place the Col A column from the R06_Table table into the Rows area of the visualization.
4. In the same Matrix visualization, place the Col B column from the R06_Table table into the Columns area of the visualization.
5. In the same Matrix visualization, place the AcrossThenDown measure into the Values area of the visualization.