When I make a scatterplot in Excel 2003, and choose Add Trendline, I have the option to show the formula in the chart. I would like to use this formula. The problem is, the only way I know how to do this is to manually type the components of the formula into some cells and manually create the formula. This is sometimes ok, but when the data underlying the scattreplot change, so does the formula. Is there a way I can make a derived trendline formula which is dynamic?

I'd be grateful for any help.