Copying data to 2nd Workbook slows down as it proceeds

I have a workbook with about 2400 rows and 70 columns of data. I then create
an empty workbook, add column headers for 10 columns. Using 5 columns of the
original workbook, I determine which rows contain data based on non-empty
cells. I then extract data from the row for the 10 columns and then place it
in the next available row in the output workbook. In the status bar I keep
track of the current row in the input workbook. The output workbook finally
contains about 3200 rows. I have Screen Updating = False. At first - up to
row 500 - it runs relatively fast and then just keeps slowing down until
about a tow per second???

The last time I propagated the output worksheet with 2900 rows and 10
columns of periods - just to try to force a size. It still did the same
thing. Any suggestions.

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Gus Evans