Individual photometric and spectroscopic temperature measures for HD 20 obtained in this work. On the abscissa either the photometric color or the spectral region that was used to deduce T_eff is labeled. Different colors indicate the different scales and methods employed (see legend and main text for details). For each T_eff that was deduced from a color index, the negligible effect of no reddening and twice the applied reddening (E(B − V) = 0.0149 mag, Schlafly & Finkbeiner 2011) is denoted by light-colored ranges behind the circles that are barely visible. The IRFM findings for HD 20 by Alonso et al. (1999b) and González Hernández & Bonifacio (2009) are shown together with the literature values by Barklem et al. (2005) and Gaia DR2. The finally adopted temperature and its error ( K) are shown by black- and gray-dashed lines, respectively.