Tom Ogilvy wrote:
If you want to do a linear interpolation, then use the Forecast function.
FORECAST(x,known_y's,known_x's)

=FORECAST(2,{10,20},{1,3})
returns 15 for example.

Also look at LINEST

These will only return linear interpolations, I was hoping to be able
to some how to access the trendline formulae that the charting function
has and use that, but this seems not to be possible :(

Best

JAG-W