Grand total problem incorrect on Power BI Matrix , How to Fix Sum of Metrics calculation

Hi RafiQLB ,

Thanks for sharing the model. I was not able to see you also have a 'Cities' Dim table that's also filtering your 2 Fact tables. So the earlier SUMX(VALUES(Products[ProductID])) logic did not consider combinations of city + date + product. As a result, totals are still incorrect especially in filtered contexts.

You may test this below 

_POS TOTAL VARIANCE (-) = 
SUMX(
    ADDCOLUMNS(
        CROSSJOIN(
            VALUES(Products[ProductID]),
            VALUES(Cities[CityID]),
            VALUES(Caln[Date])
        ),
        "@Purchased", CALCULATE([Total Purchased Quantity]),
        "@Sold", CALCULATE([Total Sold Quantity]),
        "@Variance", CALCULATE([Total Purchased Quantity]) - CALCULATE([Total Sold Quantity])
    ),
    VAR _var = [@Variance]
    RETURN IF(_var < 0, _var, 0)
)

Same logic for your negative Variance calculation. 
Hope it works:)