Your formula didn't work, it only shows the value of Aantal per transaction. I think beause there are multiple rows for one day. I edited it a bit and I think I have it working now. 

formula = 
    CALCULATE (
        SUM ( Voorraadmutaties[Aantal] ),
        FILTER ( ALLSELECTED ( Voorraadmutaties ), [Index] <=MAX(Voorraadmutaties[Index]) ),
        VALUES ( Voorraadmutaties[artcode])
    )