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tokens: temperatures and metallicities is fair, with our temperatures being an average of 161 K cooler (σ = 181 K), and our metallicities an average of 0.12 dex lower (σ = 0.15 dex). The surface gravities show a similar offset, ours being lower by 0.18 dex, and an rms scatter σ = 0.16 dex, but the discrepancies seem to be largest (by up to 0.5 dex) for the coolest and more metal rich stars in the sample. Figure 2. Upper panel: observed (solid black line) and best-fitting model (broken red line) for four representative stars in our sample of proposed flux standards. Bottom panel: ratio between model and observed fluxes. Table 1. Derived parameters and angular diameters (θ) for the proposed bright spectrophotometric A-type standards. The scatter given corresponds to the standard deviation in θ for the spectral data points in the 400–800 nm range. The uncertainty σ(θ) is derived by adding the scatter in quadrature with a 0.4 per cent error that corresponds to propagating the uncertainty in the zero-point of the flux scale (0.8 per cent or 0.008 mag). Both the atmospheric parameters from the NGSL library (Lindler Heap 2008 ) and those derived in this paper are provided. We estimate our uncertainties are about 120 K, 0.2 dex and 0.1 dex (random) and 150 K, 0.2 dex and 0.1 dex (systematic), for T eff , log g and [Fe/H], respectively (but see text for a caveats about log g for some stars). The V -band photometry derived from the NGSL spectra, and those measured from the ground and compiled by Mermilliod, Mermilliod Hauck ( 1997 ) are in the last two columns. Our conclusion about the systematics in our derived surface gravities is reinforced by comparing our results with Allende Prieto Lambert (1999), who compared the V -band absolute magnitudes, computed from Hipparcos ’ parallaxes, and B − V colours, with models of stellar interiors. Their surface gravities for eight stars in common are an average of 0.33 larger than ours (σ = 0.18 dex), and show a similar trend as we found with the NGSL values, with larger discrepancies for cooler more metal-rich stars. The comparison with metallicities from the PASTEL bibliographical catalogue (Soubiran et al. 2010 ), which compiles stellar atmospheric parameters determined from high resolution, high signal-to-noise spectra in the literature, shows, for eight stars in common, a mean offset of 0.02 dex, ours being lower, and significant scatter (σ = 0.48 dex). Our gravities are also lower than those in PASTEL by an average of 0.08 dex (σ = 0.21 dex). Lastly, our comparison with the parameters published by Koleva Vazdekis ( 2012 ) shows the largest spread, with standard deviations of 702 K in T eff , 0.5 dex in log g and 0.6 dex in metallicity. To evaluate the effect of neglecting reddening in our analysis, we have tested the consequences of adopting instead the reddening estimates provided by Lindler Heap (2008) as part of the NGSL, correcting the spectra for reddening using the mean Galactic extinction curve given by