The year period to date as % of LY period to date

I am trying to create a calculated measure in which I can get this year period to date as a percentage of last year period to date.

Example: We have sales through Jan 15 of this year (2010), I would like to get the first 15 days of January last year (2009)and compare it to this year. So I can get a percentage of this year to last year difference.

I have tried using the periodToDate with the ParallelPeriod but I still get the first 15 days of this year, compared whatever period I am in the date hierarchy for LY. If showing by Quarter it will show all of LY Q1 compared to just the first 15 days of January of this year.

I always want to compare the same number of days of this year to the same number of days last year regardless of where in the data hierarchy I am at. Even if I show Q1 I would like to compare Q1 up to current date, and Q1 prior year up to the same date.


with
member [Measures].[2010 Sales Amt] as
'([Date DM].[Fiscal - YQMWD].CurrentMember, [Measures].[Sales Amt])'
member [Measures].[PP] as
(ParallelPeriod([Date DM].[Fiscal - YQMWD].[Fiscal Year]
,-1
,[Date DM].[Fiscal - YQMWD].CurrentMember),[Measures].[Sales Amt])
select
{ [Measures].[2010 Sales Amt]
,[Measures].[PP] } on columns
,{[Date DM].[Fiscal - YQMWD].[Fiscal Quarter]} on rows
from
[DDS SKU]