Comparing a value across different snapshot weeks in a single table.

Hello KHSK 

try this measure

Newly Added Amount =

VAR PrevWeek =

    SELECTEDVALUE('SnapshotTable'[Snapshot Week], 0) -- From Previous Week slicer

VAR CurrWeek =

    SELECTEDVALUE('SnapshotTable (2)'[Snapshot Week], 0) -- From Current Week slicer

VAR PrevIDs =

    CALCULATETABLE (

        VALUES('SnapshotTable'[Oppty ID]),

        'SnapshotTable'[Snapshot Week] = PrevWeek

    )

VAR CurrTable =

    FILTER (

        'SnapshotTable',

        'SnapshotTable'[Snapshot Week] = CurrWeek &&

        NOT 'SnapshotTable'[Oppty ID] IN PrevIDs

    )

RETURN

    SUMX(CurrTable, 'SnapshotTable'[Oppty Amt])

Thanks,
 Pankaj Namekar | LinkedIn

If this solution helps, please accept it and give a kudos (Like), it would be greatly appreciated.

You'll need 2 tables to use in the slicers. You can create them like

Current Week = DISTINCT( Ops[Snapshot Week] )

Prev Week = DISTINCT( Ops[Snapshot Week] )

Make sure that these tables are not connected to the main table.

Create a measure like

New Amount =
VAR PrevOps = CALCULATETABLE(
    VALUES(Ops[Oppty ID]),
    TREATAS(
        VALUES('Prev Week'[Snapshot Week]),
        Ops[Snapshot Week]
    )
)
VAR CurrentOps = CALCULATETABLE(
    VALUES(Ops[Oppty ID]),
    TREATAS(
        VALUES('Current Week'[Snapshot Week]),
        Ops[Snapshot Week]
    )
)
VAR NewOps = EXCEPT(
    CurrentOps,
    PrevOps
)
VAR Result = CALCULATE(
    SUM(Ops[Oppty Amt]),
    NewOps,
    TREATAS(
        VALUES('Current Week'[Snapshot Week]),
        Ops[Snapshot Week]
    )
)
RETURN
    Result

NewOpptyAmount = 
VAR CurrentWeek = 10 # Insert SelectedValue(Current Week Slicer)
VAR PreviousWeek = 8 # Insert SelectedValue(Previous Week Slicer)

VAR CurrentOppties = CALCULATETABLE(
        VALUES(Snapshot[Oppty ID]),
        Snapshot[Snapshot Week] = CurrentWeek
    )

VAR PreviousOppties = CALCULATETABLE(
        VALUES(Snapshot[Oppty ID]),
        Snapshot[Snapshot Week] = PreviousWeek
    )

VAR NewOpptiesOnly = EXCEPT(CurrentOppties, PreviousOppties)

RETURN
CALCULATE(
    SUM(Snapshot[Oppty Amt])
    , Snapshot[Oppty ID] in NewOpptiesOnly
)

Change the column and variable names accordingly.