Left column: differences between the atmospheric parameters derived from spectral indices and high-resolution analysis for the MARVELS validation sample as a function of the total S/N. Right column: internal uncertainties of our method as a function of the total S/N. The upper, middle, and lower panels show the cases for Teff, [Fe/H], and log g, respectively. Stars with V < 9, 9 ⩽ V < 11, and V ⩾ 11 are shown by black, blue, and red filled circles, respectively. In all panels, the solid black line represents perfect agreement. The dotted and dashed black lines mark, respectively, the limits ±100 and ±200 K for Teff, ±0.10 and ±0.20 dex for [Fe/H], and ±0.20 and ±0.40 dex for log g. The differences between the two sets of atmospheric parameters and the internal uncertainties of the spectral indices method do not show any dependencies with S/N and V magnitude.