1) Linear fit I am running an experiment to find the linear relation between displacement (X) and voltage reading (V) of the measurement, when fitting a linear line to my measured data, such that: V= m*X + b; Based on the following links http://en.wikipedia.org/wiki/Regression_analysis (under Linear regression) and http://en.wikipedia.org/wiki/R-squared ( under Definitions) I can find the The standard errors of 'm' and 'b' parameters, Sm and Sb, respectively. and R-squared So the Uncertainty of my measurement is : m -/+ Sm and b -/+ Sb But I would like to use the fit in the following way : x=(V-b)/m How can I relate the fit error to this form of the equation ? 2) Non-Linear fit In the second experiment I have the following cubic fit: X= a3 * (V ^3) + a2 * (V ^2) + a1 * (V) + a0 How can I find the uncertainty of a3, a2, a1, and a0 ? because I could not find any reference for doing so. Can I use the same formula I used in the linear case to find the R-squared here for the non-linear fit?