Formula to show/reference selected value by slicer/timeline

Hi,

Herewith the document + data.

So, I have a timeline connected to a pivot table.
So in my case: I select a month within a year, say december 2016 and then I get total revenue februari 2016.

However I would also show the total revenue for year - 1, in my example februari 2015.

How can I manage to do this?

Best,
Maurice