I have two sets of experimental data: $\phi(t)$ and $I(t)$. In theory they are related to each other as: $\phi(t) = nI(t) $. By fitting these curves together I can find the value of $n$ (which is a constant). I can calculate the error of this fit using residue and covariance.
Now, for each point $t$ of my data sets I also have error of $\phi(t)$ and $I(t)$. How to propagate this error through the fitting procedure, so the final error of the $n$ parameter is also influenced by them?