Distribution of the RUBIES parent sample (spanning the full EGS and UDS NIRCam area of ∼300 arcmin²) and of the targets selected for spectroscopic follow-up, shown in the space of parameters used to define the selection function: photometric redshift, F444W magnitude, and F150W−F444W colour. Top panels show the absolute source counts, while bottom panels show the fraction of observed targets with respect to the full parent sample. The RUBIES selection is strongly biased (as intended) towards red sources and preferentially targets brighter sources at z_phot>3, although the majority of the observed targets are still faint (F444W>26) and relatively blue (F150W−F444W∼0).