Prba wrote on Fri, 24 Feb 2006 07:37:27 -0800:

P Question:
P I have 2 dataseries in a XY Scatter Chart. I want a one
P (common) regression line for both series, not one for each
P series. Is that possible?

I wonder why you would want that? Why not just combine the two
sets of data when calculating the regression or plotting a trend
line? If you really want the two separate series to be plotted
and not the combined one, you might use a background color for
the combination after adding the trendline.

James Silverton.