Photon noise error in the measurement of the CCF center of single observations vs. S/N at 490 nm for our sample of open cluster targets observed with HARPS. The overall RV errors are typically distributed around 1–4 m s⁻¹ and range from 42 cm s⁻¹ to 119 m s⁻¹. The overall S/N distribution peaks around 20–40 and ranges from 2.4 to 223. Black filled circles are the selected data, and gray crosses are the discarded ones, all identified from a visual inspection of the CCFs. Black open circles depict the data with S∕N < 10 that were also discarded and this threshold is represented by the vertical dashed line.