Our determined metallicities for ten of the M dwarfs in our sample compared with three photometric calibrations, as well as values adopted by RA12 and Ma15. The differences are plotted against our derived metallicity and the effective temperature. The size of an uncertainty of ±0.1 dex is indicated by the black symbol in the bottom right. The dashed lines are there to guide the eye which points belong together, not to indicate a trend.