Least square value of x and y values of a fitted model

I'm attempting to determine the R-squared value of a fitted model compared to experimental data using the vertical and horizontal error values. I can only find methods for the vertical value, ANY help would be greatly appreciated. The horizontal value is proving especially difficult.

[Scarlett]

This is very nonlinear model as well, and polyfit was not used to find it.

Answer 1

[the cyclist]

These are known as errors-in-variables models, http://en.wikipedia.org/wiki/Errors-in-variables_models. I am not personally familiar with the techniques here. You might find some information in this old thread:

http://www.mathworks.com/matlabcentral/newsreader/view_thread/137563

[Scarlett]

Thanks for the help, doesn't look like those are terribly to me though. The model was found using the fminsearch algorithm if that helps at all. . .