Result of the benchmark of the excitation calculation. The upper panel shows the results for a HCO⁺ abundance of 10^-9 relative to H₂, the lower panel for an abundance of 10^-8 relative to H₂. The plots on the left display the normalized level population of the first eight levels, the plots on the right show beam-averaged intensities. The black lines give results obtained using the RATRAN code, and the red dots/lines show results derived by this work. The gray shaded area indicates a 30% range to the RATRAN solution.