y exp,i denotes the experimentally observed value at i, y calc,i the estimation of the observed value according to the model parameter and e i the residual at each data point. The parameters θ are henceforth referred as to θ in case they are the best-fit parameters after least-squares optimisation. Characterisation of the fit can be realised using the standard deviation of the residuals σ f it (eq. 30), SE y (eq. 31) and χ 2 (eq. 32): 15