An extraordinary large spreadsheet
 

I have a large spreadsheet that uses about 30 pivot tables stored in one tab.
Other tabs are linked to that data. Whenever I have to change anything in the
spreadsheet: changing a formula or adding a row, it takes about 7 minutes to
calculate. I switched it to Manual calculation and, after changing a few
things I hit recalculate. The program crashed. I could not believe it since I
have Pentium 4HT 3.6 GHz and 1 gig ram. Can someone advise on how to deal
with the problem?
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Sergei D