Compare month to previous months

[enlamparter]

I'm trying to compare data from one month (selected by a slicer) to the average of the prior three months but my measures are not working properly.

My current function is as follows:

_dax%_compare = CALCULATE(DIVIDE([_dax_totalHours_by_Function],tbl_Data_Source[_dax_TotalHours_byOrg]),DATESBETWEEN(_ref_Periods[_col_date],DATEADD(FIRSTDATE(_ref_Periods[_col_date]),-3,MONTH),DATEADD(LASTDATE(_ref_Periods[_col_date]),-3,MONTH)))

To start, I've also tried to just generate the value for the prior month, but even that doesn't work. In every case, the value it generates is the value for the current month. Not the previous, as desired.

When I just enter:

DATEADD(lastDATE(_ref_Periods[_col_date]),-3,MONTH)

I get the date I would expect, but for some reason it doesn't work when I plug it in as a filter on the data.

If anyone can even help me even generate the value for the prior month, I would much appreciate it.

[Greg_Deckler]

Take a look at my TITHW Quick Measure here:

https://community.powerbi.com/t5/Quick-Measures-Gallery/Time-Intelligence-quot-The-Hard-Way-quot-TIT...