Carolyne wrote on Tue, 11 Jul 2006 13:05:02 -0700:

C Is it possible to get exact values from a graph that isn't
C one of your data points? When I graph nonlinear variables is
C there some type of formula I can type in to get me an exact
C x value for a specific y value. For example i have x values
C of 0, 1, 2.5, 5, 10.... and y values of 100, 79, 55, 32, 12.
C If I want to know what x equals when y=50 how do i go about
C doing that? I know that I can't use the standard y=mx+b
C because my data is not linear... any suggestions?? I've been
C trying to figure it out for a couple of weeks and its
C starting to drive me crazy. Ive looked into a couple of
C other graphing programs (Igor Pro, GraphPad Prism and Delta
C Graph 3 and they have been no help either!)

Despite its name, FORECAST can be used to get points internal to
a graph.

James Silverton.