Unfortunately that equation can get a little hairy and can exceed some of the
limitations for formulae. At least any formula that I have seen.

"Ron Rosenfeld" wrote:

On Thu, 9 Oct 2008 14:46:11 -0700, Brazell
wrote:

The problem with forecast is that it does a linear regression of the line
through the points so that the line may not actually cross any of the points.
What many of us would like is a function that draws a straight line between
each individual point and extrapolates the value based on each line segment.

Just set up your formulas to use the two points that straddle your unknown.
--ron