Maximum likelihood method (MLM) velocity errors as a function of the S/N per pixel for measurements of υ_los for individual VLT/FLAMES LR8 spectra of likely RGB member stars in the Sextans dSph, with G < 19.7. The blue squares are stars that do not pass the velocity quality criterion and the red stars ones that do not pass the EW quality criterion; some fail on both. The vertical dotted red line indicates the acceptable limit (S/N > 10) that is applied to the final selection of υ_los measurements, bearing in mind that the blue squares and red stars were removed before the cut.