My method works, so looking for something more accurate or faster.
The least squares thing is how you measure how good the curve was. not how to create it. I ignore least square and use abs-values as it is more important for me to match the curve near zero than at the extreme positive end (10LPM and more) as we're never there.
The main page uses roots, but I don't get the benefit of multiple crosses of X and Y axis, just 0,0.
Lagrange Interpolation Polynomials look like fun:
http://www.wmueller.com/precalculus/.../lagrange.html
I could then use least squares to automate the simplication of the polynomial and wiggle it around to find the best fit.