Average of running total over a given period

[MadsLarsen]

Hi. I want to find the average of a running total over a given period.

I've got a column increasing and decreasing inventory quantity by +-XX for a range of products over time, so i've found the the total inventory over time by a running total.

Inventory Running Total =

CALCULATE(

     SUM('Komponent Omsætning'[Quantity]);

     FILTER (

     ALL ( 'Date'[Date] );

     'Date'[Date] <= MAX( ( 'Date'[Date] ) )

    )

)

The running total must start from the beginning of time to get the actual inventory, but i only want the average over a given period. When i try to calculate the average over any given period, it only includes the changes in that period, without the offset from all previous time. The average could therefore turn out to be i.e. -3 instead of 20.5.

So how do i determine the average including the offset from all previous dates?