Averaged relative abundances to H₂ for electrons, HCO⁺, and N₂H⁺ plotted for the all four stages. The observed values are shown as solid lines, the modeled values are depicted as dashed lines. The electron abundances are plotted in red, N₂H⁺ abundances in black, and HCO⁺ abundances in blue. The error bars for both the model and the observational data are a factor of about 3 (not shown).