How to Define AVG in measures?

How to Define AVG in measures?

see:

http://forums.microsoft.com/MSDN/ShowPost.aspx?PostID=390791&SiteID=1

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I don't understand above form. can you please check this what mistake i did.

Avg({descendants([Result],[Year].[Month].[Day])}, [Measures].[Ambient Temperature])

Measure and Dim structure is below:

1st Dimension Name: [Dim Tests ASM]

It Attribute: [Result], [StationName], [UnitID]

2nd Dimension Name: [Dim Time Key]

It Attribute: [Year], [Month], [Day]

Measures : [Measures].[Ambient Temperature]

Regards,

Dinesh Patel