In equation 34, K refers to the number of parameters, N to the number of data points and F α N,N-K to the critical value in the Fdistribution for the given degrees of freedom and desired confidence interval. A graphical interpretation is given in Fig. . The sum of squares has a minimum at SSE( θ ) and can be decreased to θ i,-or increased to θ i,+ while the error is smaller than SSE max .