Ah, but what's in those 18,000 cells? Array formulae, links to other workbooks, etc. can all have a significant impact on performance.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

Thanks guys for helping.

THere is one column that counts up then restarts when a value in the next row changes and another column that decides whether to show blank or a number dependent upon whether or not the next row contains a particular walue. Otherwise it is all passive data. I tried the manual calculation trick, no discernable difference

Nothing onerous