Comparison between HFR oscillator strengths (log gf) and previously published values for Hf I–III ions. Previous data were taken from Duquette et al. (1986) for Hf I and from Den Hartog et al. (2021), Lawler et al. (2007), Lundqvist et al. (2006), and Bouazza et al. (2015) for Hf II. Two different semi-empirical approaches were used in the latter reference based on a parametrization of the oscillator strengths (OSP) and on a pseudo-relativistic Hartree-Fock model including core-polarization effects HFR+CPOL from Malcheva et al. (2009) for Hf III, respectively.