You may try the following custom format for the field:
[hh]:mm

Hope this helps,
Miguel.

"Béatever" wrote:

Hi,
I've got an excel sheet (2002 SP3) with calculated durations (end time -
start time). When I put these in a Pivot tabel, the duration can not be
calculated when exceding 24h (f.i. a sum of 27,5h is shown as 3:30h. When
looking into the content of the cell, I see 1/01/1900 3:30:00). Formatting
does not help. Can somebody help me?