Hα/Hβ, Hγ/Hβ, and Hδ/Hβ line ratios in logarithmic scale, from top to bottom. The first four values of each row (filled circles) correspond to the theoretical values obtained using (log T_e, log n_e) = (4.0, 3.4), (4.0, 4.4), (4.2, 3.4), and (4.2, 4.4), respectively. The horizontal lines correspond to the value obtained for (4.0, 3.4). The following nine values correspond to the de-reddened line ratios obtained by GR22 (diamonds) and UO22 (stars) for the nine PNe considered in both papers.