Residuals between the metal abundances determined here and from literature are plotted against the chemical elements. Filled symbols mark results derived from UV-spectroscopy (squares, Fontaine et al. 2006; diamonds, Blanchette et al. 2008; triangles, O’Toole & Heber 2006), open symbols results derived from optical high-resolution spectra (circles, Edelmann et al. 1999; upward triangles, Napiwotzki et al. 2001; squares, Pereira & Jeffery 2008; diamonds, Heber et al. 2000; downward triangles, Przybilla et al. 2006). The dashed horizontal lines mark our statistical uncertainty estimate (± 0.3   dex).