The result is shown in Fig. 5.4. The residual at each data point is plotted in the lower sub plot for each fit and the norm of the residual is also shown on the plot. Note that although the two curves are visually almost indistinguishable over the range of the data, the norm of the residuals for the cubic fit is an order of magnitude lower than that of the quadratic fit, and therefore, you may like to chose the cubic fit in this case.