Line ratios normalised to the Huα line, compared to the local excitation (KF11) and Case B models (Storey & Hummer 1995). Error bars are omitted, since the overall uncertainty is dominated by the discrepancy between the two extinction curves (triangle and circle markers). Solid markers represent detections with S/N > 5, while open markers show detections with 3< S/N < 5. Panels display models for temperatures of 10 000 K (left) and 7500 K (right), and for the KF11 model we also include different density values ranging from n_H = 10⁹ to 10¹² cm⁻³. We show the Case B model for a single electron density value, N_e (in cm⁻³), as this parameter appears not to change predictions significantly. Lines in the x-axis are organised by increasing wavelength.