Individual line profiles for the disk-centre intensity calculated from the half-resolution regular grid and an irregular grid with three million sites sampled from log(N_H)⁻²T^−2/5. Every black line corresponds to the brightness temperature from a column in the atmosphere. The spatial average over all columns is represented by the red line. The dashed blue lines indicate the wavelength positions of the blue wing at 121.558 nm (or −27 kms⁻¹) and line centre λ₀ at 121.568 nm.