Trendlines for Graphs?

[scottmorley]

I am wondering if there is a way to add trendlines to an existing graph (i.e. similar to the functionality in MS Excel). My immediate need is to add a simple linear trendline. Not only would it be useful to add a trendline on an existing graph, it would be great to be able to create a separate, trendline-only graph based upon data included in the “normal” graph.