Excel 2003 drawing Trend lines on a chart for a given set of point

[BEETAL]

I have encountered a very stupid result while drawing a Trend line on number
of points given on a chart. The stupidity reflects in the resulting equation.
The resulting equation gives rise to Y values, for the same X-values it used
in the first place, very divergent from the Y values that it is supposed to
predict. Has any body encountered this problem before?

What is the algorithm that is used by Excel to draw the Trendlines,any body
could educate me,please?

 

[Mike Middleton]

beetal -

Such differences are often due to (1) using a Line chart type instead of an
XY (Scatter) chart type, in which case Excel uses 1,2,3,... for the x values
or (2) not showing enough significant digits for the trendline equation. If
you think your results have another cause, please describe your data,
trendline type, and results in detail.

As far as I know, the algorithms implement ordinary least squares, in some
cases using transformed x or y values (or both).

- Mike Middleton
http://www.DecisionToolworks.com
Decision Analysis Add-ins for Excel