Untitled

Value Difference = 
SUMX(
    DISTINCT(UNION(
        VALUES('Aggregated Value_SQL'[BMU]),
        VALUES('QM & Generation sent out_SQL'[BMU])
    )),
    VAR AggValue = CALCULATE(
        SUM('Aggregated Value_SQL'[+ve Agg Value]),
        'Aggregated Value_SQL'[BMU] = EARLIER('Aggregated Value_SQL'[BMU])
    )
    VAR GenSentOut = CALCULATE(
        SUM('QM & Generation sent out_SQL'[Generation Sent Out]),
        'QM & Generation sent out_SQL'[BMU] = EARLIER('Aggregated Value_SQL'[BMU])
    )
    RETURN AggValue - GenSentOut
)