issue in a crosstab

[philelmousse]

Hello,

I have a crosstab built like this :

                                   TimeDimension
Dimension1 Measure  Cells

I would like to create an "average" measure under TimeDimension depending on the number of days of the period in "TimeDimension".
But If I add a query item under TimeDimension like that :

total(currentMeasure within set [TimeDimension])/
extract(day,_last_of_month([LOGICAL LAYER].[Fact].[HDATE]  ))

My entire crosstab returns blanks...

Do you have any idea to make that ?