Chris -

In general, lines connecting points of an XY (Scatter) chart will appear
smooth only if you use a very large number of points or if you choose the
Smoothed Line option or if you use Add Trendline.

To get a smoothed line, after you create the chart, select the data series
by clicking on one of the points, and choose Format | Selected Data Series |
Patterns | Line.

To show more significant digits after you add a trendline, select the
text-box-like object containing the fitted equation, and click the Increase
Decimal button repeatedly.

There are worksheet-function equivalents for each of the Add Trendline
functions. Tushar Mehta has some explanations at
http://www.tushar-mehta.com/excel/ti...efficients.htm

For interpolation of the Smoothed Line option, see the links provided by
Jerry W. Lewis.

- Mike
www.mikemiddleton.com

"chris" <cpaul@suffolk.lib.ny.us> wrote in message
news:1150764697.790960.286230@u72g2000cwu.googlegroups.com...
> Hello Mike,
>
> I'm not using any of the methods you mention. I enter the x's in
> one column and in the next column, the y's associated with each x. I
> invoke a simple scatter plot using a standard chart, and grab the data
> range I just entered. Then I hit "finish". Excel draws a smooth curve
> that passes thorugh each point.
>
> I was unable to find the "Smoothed Line option (Format Data Series
> | Pattern | Line)". How do I access it? I'm using excel 2003.
>
> Thank you for pointing out the that trendlines can be power law or
> polynomial, though. And wow! Excel will even print the equation it
> uses to match the curve. Except... It's wrong! I used y = x^1.5 and
> selected a "power" trendline. The trendline was drawn perfectly, but
> the printed equation was y = x^2. Doesn't seem to like decimal
> points???
>
> If I could only call the curve it generates (either directly from
> the data or as a trendline) as a function!
>
> Regards,
>
> Chris
>