Hi Chris,

From your post it sounds like you are talking about the line that excel
provides to link your data in an XY scatter chart.

You can add a trendline to your data series that offers a lot more
functionality. Namely better fit to your data, the ability to forecast
values forward and backwards, the ability to calculate values of
y for a given x or vice versa, etc. etc.

Is this more along the lines you are thinking? If so post again with some
more detail.

Regards
Martin