Distribution of ∆= υ_{rad,Nacre,ref}− 〈υ_rad,Nacre〉_masks (binwidth = 0.02 km s⁻¹) where υ_rad,Nacre,jis either the velocity υ_{rad,Nacre,best} returned by the bestmask NACRE CCF (see text; red) or a randomly chosen NACRE velocity υ_{rad,Nacre,rand} (black). Left: HR10 setup. Right: HR21. The mean, standard deviation and interquartile range of each distribution, expressed in km s⁻¹, are: (0.17,0.59,0.22) for HR10 and ‘best mask’; (0.01,0.77,0.39) for HR10 and ‘random mask’; (0.02,0.38,0.33) for HR21 and best mask; (0., 0.50,0.41) for HR21 and random mask. The number of objects in a given selection is indicated in the legend box. The distributions are narrower for υ_{rad,Nacre,best} than for υ_{rad,Nacre,rand}.