Comparison of the GLS periodograms when using two different masks. Top: GLS periodogram of the EV Lac 2010 RV data set obtained with the full mask. Bottom: same, but using the 2010-trained best sub-mask. The significance of the peak at the stellar rotation period decreases in the latter case, confirming the mitigating benefit of using the sub-mask derived from the randomised selection. There is a peak at30 d showing an increase in power when the best sub-mask is applied. A period analysis of the window function (VanderPlas 2018) reveals that the peak is most likely due to the observing span (~2 months) and cadence of the 2010 data set.