Top panel: distribution of the number of observations per star in sample R. Bottom panel: number of HERMES observations vs. time span of the RV observations for the comparison sample of Kepler/CoRoT giants (sample R; open squares). Most of the stars have three observations spanning 300 to 900 d. Red crosses correspond to the re-sampled data of sample S1 (denoted ‘sample S1’) with N_obs and Δt modified to mimic the distribution of sample R (see Sect. 5.5).