Phase-folded plot of the 2008 RV time series (26 observations) of DS Leo computed with (from top to bottom) the full mask including telluric windows, the 2008-trained best sub-mask, the worst RMS-based sub-mask, and the worst K-based sub-mask. A stellar rotation period of 13.57 ± 0.04 d was used, computed via GLS periodogram, as described in Sect. 2. Second panel: remarkable reduction of both the RV dispersion and semi-amplitude, reaching the instrumental limitation of NARVAL (~30 m s⁻¹). The third and fourth panels display an RMS-based selection that is affected by different sources of dispersion (telluric contamination in particular) and an ineffective K-based selection following the low level of activity of the star, respectively.