Please see if the attached could be a first step for you.
I used the INDEX function to count back from the last date.
IF [Index]>(WINDOW_MAX([Index]) - 4)
THEN ATTR([Upper Int])
Similarly for LowerInt
This only returns values for those dates, so don't need to place
a filter, but just put the calc on the Measure Values shelf
To filter for a particular date, I think you need to use the MAKEDATE function:
THEN [Upper Int]
211412filter.twbx 12.6 KB