Previous Week Inventory - this week Sales

Hi,

I am not sure how your semantic model looks like, but I tried to create a sample pbix file like below.

Please check the below picture and the attached pbix file.

WINDOW function (DAX) - DAX | Microsoft Learn

expected result measure: =
VAR _startdate =
    CALCULATE ( MIN ( data[week_end_date] ), REMOVEFILTERS () )
VAR _startinginventory =
    CALCULATE ( SUM ( data[inventory] ), data[week_end_date] = _startdate )
VAR _previousinventorycumulate =
    CALCULATE (
        SUM ( data[inventory] ),
        WINDOW (
            1,
            ABS,
            -1,
            REL,
            ALL ( data[week_end_date] ),
            ORDERBY ( data[week_end_date], ASC )
        )
    )
VAR _salescumulate =
    CALCULATE (
        SUM ( data[sales] ),
        WINDOW (
            2,
            ABS,
            0,
            REL,
            ALL ( data[week_end_date] ),
            ORDERBY ( data[week_end_date], ASC )
        )
    )
RETURN
    SWITCH (
        TRUE (),
        MAX ( data[week_end_date] ) = _startdate, _startinginventory,
        _previousinventorycumulate - _salescumulate
    )