Diagram representing EW(Hβ) vs. Q(H₀) for inner (red diamonds) and outer (blue crosses) observed H II regions. Overplotted solid lines are predictions by PopStar models for the evolution of EW(Hβ) and Q(H₀) depending on age for two different metallicities: Z = 0.008 (black triangles) and Z = 0.02 (green asterisks) and four different ionising cluster masses, indicated in the plot in units of solar masses. Following the model prediction from top to down, each symbol indicates an evolution of 1 Myr, with a starting age of 1 Myr. Starburst99 model predictions are overplotted for the same metallicities using the same colour code, with dotted lines for M_up = 100 M_⊙ and dashed lines for M_up = 30 M_⊙.