I want to add three days sales as a calc

I want to add three days sales as a calculated member using Crystal Analysis. Following works perfectly for a single days sales. ([Time].[Year].&[2008].&[QTR-2 - 2008].&[12].&[1/12/2007],[Measures].[Sales]) But if I use the following to get 3 days sales using the above range formula then it fails. ({[Time].[Year].&[2008].&[QTR-2 - 2008].&[12].&[1/12/2007] : [Time].[Year].&[2008].&[QTR-2 - 2008].&[12].&[3/12/2007]},[Measures].[Sales]) Can you please tell me how I can do this in Crystal Analysis which uses MDX syntaxes?