In Excel 2007, if you apply a fourth-order polynomial to any set of X-Y data
on a scattergram AND force the intercept through 0, the correct fitting
equation is displayed. However, when you re-load the workbook after a save,
the fourth order term is completely removed from the equation that is
displayed on the chart. This can lead to incorrect results if subsequent
calculations depend upon the displayed equation (the underlying 4th order
equation that fits the trendline appears to be OK, it is only the equation
displayed that is incorrect). The problem doesn't occur if you do not force
through zero and does not occur in Excel 2003.

You can confirm this bug with any set of X-Y data you wish to create. A
similar bug has been noted on the web since January, I think, but I cannot
find any site to indicate that Microsoft has addressed the issue.
--
rday

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