Pivot Table - Blank SubTotal in Calculated Field

[Guilk]

Hello,

I looked around without success.

In a Pivot table, there are 2 existing fields, linked to a spreadsheet, 'N'
and 'N-1' for items split in 2 groups.
I created a Calculated Field "Y/Y"= 'N'/'N-1'-1 to simply get the variation
between the 2 years.

N N-1 Y/Y
Group 1 a b %
c d %
Total Group 1 U V
Group 2 e f %
g h %
i j %
Total Group 2 W X
Grand Total Y Z %

The Y/Y results are corrects for each items and the "Grand Total".
The problem is that nothing appears for the Subtotal Y/Y variation.

Could you help?

I use Excel 2000. Tks a lot.