Mike Middleton wrote:
I forgot to mention that, although "I have used Solver for fitting
4-parameter functions (albeit with only a dozen data points), and I've
always used the default settings with success," I usually have to try a
variety of starting points for the parameters before I eventually get an
appropriate Solver result.

- Mike
I think I'm pushing Excel a little too hard
I have 6000+ data points fitted to am equation with 9 adjustable
parameters (exponents etc ..).
It takes Excel ~ 10 sec to recalculate the cells and about 6 sec to run
the macro.
I like to use solver interactively - adjusting the starting points
calculation method etc...
I can take some pretty good educated guesses about the starting
parameters, On similar problems it take at least 3-6 runs before I get a
reasonable estimate. - My main problem with this problem is the time it
takes to run.

Of course I could always ask for a faster computer ;-)
Gregg