actually came up with
=Nz(Sum([StockIn]),0)-Nz(Sum([StockOut]),0) for my total stock count and
=-Sum(([Location]="1")*(Nz([StockIn],0)-Nz([StockOut],0))) for warehouse1
=-Sum(([Location]="2")*(Nz([StockIn],0)-Nz([StockOut],0))) for warehouse2
Works perfect
Problem solved