Open symbols: EW measurements for the indicated diagnostic lines using the various high-resolution spectra available (circles: HIRES; triangles: HARPS-N; squares: HORuS). Gray rectangles: predicted range of EWs from FASTWIND models with the same T_eff and log g and a range in abundance ±0.15 dex around the reference value (solid horizontal line; see Table 1). Right panel, including the predicted EW of the O IIλ4414 Å has been included for reference to indicate that the non-detection of O II lines does not necessarily imply a low oxygen abundance.