Illustration of the influence of the parameters n_e and L on the optimal value found for T_e, for Cygnus A. The purple histogram represents all the values of T_e that give ${\chi }_{\mathrm{r}}^2(T_{\mathrm{e}})-{\chi }_{\mathrm{r},\mathrm{o}\mathrm{p}\mathrm{t}}^2<30\mathrm{\%}\times {\chi }_{\mathrm{r},\mathrm{o}\mathrm{p}\mathrm{t}}^2$. The coloured curves represents the values of T_ethat verify the condition while n_e is fixed at a given value. The snapshot on the right panel is a focus on the curve with n_e = 0.016 cm⁻³. The gray curves represent the values of T_e that verify ${\chi }_{\mathrm{r}}^2(T_{\mathrm{e}},n_{\mathrm{e}}=0.016{cm}^{-3})-{\chi }_{\mathrm{r},\mathrm{o}\mathrm{p}\mathrm{t}}^2<30\mathrm{\%}\times {\chi }_{\mathrm{r},\mathrm{o}\mathrm{p}\mathrm{t}}^2$ while L is fixed at given values.