Line-intensity ratio of the Lyα doublet for selected H-like ions as a function of the plasma column density calculated with CLOUDY. The absolute value of N_H changes for different plasma environments, as the line optical depth is converted into N_H using the chemical abundance, charge, and level populations of the simulation. CLOUDY provides Lyα₂ + M1 as a blend for Fe XXVI only. For the other one-electron species, these line must be obtained separately in CLOUDY and summed by hand.