HR diagram of the 1420 candidates with a colour code corresponding to their stability level 3σ_RVS. The less stable stars, with 3σ_RVS > 300 m s^-1, are indicated as black points. Those are not suitable for calibrating the RVS instrument. The HR diagram is divided into four parts corresponding roughly to turn-off, main sequence, subgiants, and giants where median RV scatter, and the fractions of stable and variable stars have been evaluated (Table 6).