Analysis of H I recombination line ratios. Left panel: transitions to lower levels 6 and 7 for H II template spectrum, comparing H I emission line ratios between observations and theory. Labels next to each data point indicate the transitions. The Cloudy model with foreground dust correction applied (Cloudy + FG dust) is shown assuming the largest value for the Orion Bar foreground (A(V) = 1.9), making it clear that the effect is small. Right panel: zoom-in to better show the deviations between the observations, the Case B model, and the Cloudy model. Bottom panels: observed line ratio divided by theoretical line ratio, for the three models as coded by the legend. Error bars: Uncertainty due to local noise (black) and with the 3% systematic calibration uncertainty added (gray).