SSAS,how to write a calculated member?

my mdx statement as follows.I want to use it to create a calculated member.I searched the forum.

http://social.msdn.microsoft.com/Forums/zh-TW/sqlanalysisservices/thread/964ac042-9516-452d-9524-7067a7dfff67

so,I try to create 3 calculate sets,[max sales amt],pro,dayc,then create a calculated member  ([max sales amt],pro*dayc).

but the result is null.                        

 
WITH MEMBER [Measures].[max sales Amt]
AS
 MAX(  
      
      {
       ([date].[day],[area].[city].CHILDREN)
      } ,[Measures].[sales Amt]
       )  
SET Pro
AS {
     [area].[province].CHILDREN
    } 
SET dayc
AS {
     [date].[day].CHILDREN
    }        
SELECT 
 NON EMPTY {
   [Measures].[max sales Amt]
 }
 ON columns,
 NON EMPTY {
  Pro*dayc
 } ON rows
 FROM [CUBE]