Previous Month using Set Analysis

[G_B]

Hi all,

Have been through countless similar topics, but can't seem to get this simple expression working.

Dimensions in the example are Month, Area, Colour. I have these in a straight table, and want to display two measures: Average Score and Average Score (previous month). Attempted expressions for the second measure are:

avg({$<[Month]={"$(=Date(AddMonths(Max(Month),-1),'DD/MM/YYYY'))"}>} Score)

and

avg({$<[Month]={"$(=Date(AddMonths(Max(Month),-1)))"}>} TOTAL <Area,Colour> Score)

Expected result is:

Have attached a .qvf with the example.

Thanks in advance