Mass functions of the α Per (bottom), Pleiades (middle), and Praesepe (top) clusters scaled to a volume of one cubic parsec and a logMass bin of 0.1 using isochrones of 90 Myr, 125 Myr, and 600 Myr, respectively. Error bars represent the Poisson noise. The field mass function from Chabrier (2003) is overplotted as a thick red line and normalised to the maximum value of the observed mass function at ∼0.25 M_⊙.