Thanks Lei, unfortunately that wont quite do it.
I would like the mark for 2017/teal line to be the difference between sales in dec 2016 and sales in jan 2017 (43 971 - 96 999 = -53 028). and then do a running sum of the monthly diff forward.
I'm not completly sure about what numbers the calc in your picture provides, but it doesn't add up
Sorry for the late reply!
It took me time to try using one single table calculation to achieve the running difference.
Thus, I use data blend instead, to fetch the Dec sales of the previous year, from the secondary data source.
I attached the sample workbook.
This is a very simple sample, because I only defined year in the relationship definition.
In your real case, there might be more dimensions to add to.
Please feel free to ask if there's any unclear points.
Example.twbx 1.4 MB
I went with a similar approach where I used a lookup with datepart to find last years December and calculated the diff from that. Will have a look at your solution aswell