Evolution of W(Hβ) (top), W(Hα) (center), and W(Brγ) (bottom) with age for our models adopting an instantaneous burst star formation history (with an initial mass of 10 ⁶  M _☉) and a Kroupa IMF (α = 2.3 for 0.5  M _☉–100  M _☉). The models span the five metallicities available from the Meynet et al. (1994) stellar evolutionary tracks as well as the z = 0.014 evolutionary tracks of Ekström et al. (2012), and adopt rotation rates of v _rot = 0 (solid lines) and v _rot = 0.4 v _crit (dashed line).