Thanks for replying.

I tried to create a Calculated Measure on sum(filter([CreatedDateTime].currentmember,(([Measures].[DurationSum])>0)))/count(filter([CreatedDateTime].currentmember,(([Measures].[DurationSum])>0))) and AM gave syntax error - token not valid :

sum(filter([CreatedDateTime]V.Vcurrentmember,(([Measures].[DurationSum])>0)))/count(filter([CreatedDateTime].currentmember,(([Measures].[DurationSum])>0)))

So I tried

sum(filter([CreatedDateTime].allmembers,(([Measures].[DurationSum])>0)))/count(filter([CreatedDateTime].allmembers,(([Measures].[DurationSum])>0))) , which the Value Expression...

See Microsoft MSDN Library Article "Extending Excel OLAP Functionality"

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnexcl2k2/html/odc_xlextendolap.asp