Left: map of the [O iii] λ4363/λ5007 intensity ratio as a function of electron density and temperature, obtained with the plotImage() command. Right: theoretical contour plot for the simultaneous determination of T_e and N_e with the [O iii] λλ4959,5007/λ4363 (mainly horizontal curves) and [O iii] λ52μ/λ88μ (vertical curves) intensity ratios as a function of electronic density and temperature, obtained with the plotContours() command. The levels are numbered with the log of the ratio.