The different [Fe/H] calibrations from Bonfils et al. (2005) a, b), Johnson & Apps (2009) c), Schlaufman & Laughlin (2010) d), and the calibration determined in this paper e). In each upper panel, the blue/black dots represent the data points. The black line depicts a fit to the data except in panel a), where the calibrated [Fe/H] is shown as isometallicity contours. The lower subpanels show the difference between the calibrated and the spectroscopic metallicity. The black dashed lines represent the null value, and the red dotted line represents the mean difference for that calibration.