Rolling Average based on specified number of day difference.

Customer want to calculate the rollowing average based on 14 days difference.Below is the details shared by customer:-

I would like to calculate a Rolling Average for a particular field for the last 14 days. There is not an entry for every day in the table, so there are missing days. I would like the Rolling Average to only calculate on days that are within the 14 days, so if I have 2 entries in the last 14 days, it should just be the average of those 2 days.

The calculation I'm trying to use is as follows

Avg([Value]) OVER (LastPeriods(14,[Date])

where "Value" is the field I want to return and Date is the column that has the date of the record.

When I do this, the calculation looks back over the last 14 records and returns an average of those, instead of the last 14 days and just including data from those records.