Average sample results of the latest N dates

[sedjackob]

Hi. I have a table containing 3 columns:

1. Location
2. Sample Date
3. Transmittance % value

I've added the table to the Data Model in PowerPivot.
I need to summarize each location with the average Transmittance% from the latest "N" sample dates.

For example, the average trans% for location "A" from the latest "3" sample dates is 9.22
For example, the average trans% for location "B" from the latest "3" sample dates is 22.22

I need to do this in PowerPivot (DAX) to be able to use it in PowerView. Any help would be really appreciated.