Average stock through movements

HI legrand

I think this is getting pretty close to your spreadsheet.

I created a new calculated table that I could add missing dates and apply a running total to.

New Table = 
VAR Date1 = GENERATE(CALENDAR(DATE(2017,10,1),DATE(2017,12,1)),VALUES('Table1'[Article]))
VAR Step1 = SUMMARIZECOLUMNS('Table1'[Article],'Table1'[Date],"Q",SUM(Table1[Quantity]))
VAR Step2 = NATURALLEFTOUTERJOIN(SELECTCOLUMNS(Date1,"Date",[Date]+0,"Article",[Article]),SELECTCOLUMNS(Step1,"Date",[Date]+0,"Article",[Article],"Quantity",[Q]))
RETURN  ADDCOLUMNS(Step2,"Column to Average",VAR s = CALCULATE(SUM('Table1'[Quantity]),FILTER('Table1',[Date]<=EARLIER([Date]) && [Article] = EARLIER([Article])))return if(s=BLANK(),0,s))

This gave me a column that I could easily average using a visual

.

Here is a link to a PBIX file that contains your data, my code and the visual

https://1drv.ms/u/s!AtDlC2rep7a-oX7_Ag9RNSNZVZnA