That's hard to answer without knowing your data model a bit more detailed. Could you upload a small sample QVW?
You can try something like
=Sum( If( CodeArt = Article, Qnty))
but this may not work as expected (but it's even not 100% clear what you are expecting here). Depending on your data model, the possible values of both dimensions can differ, also the record set for measure Qnty can be different in the context of chart1 compared to chart2.