Transmission plot, i.e., photons detected on the GRAVITY FT receiver, per telescope and per second, as a function of the K-band magnitude (tracking ratio > 80%). The magnitudes of the targets are obtained from SIMBAD. Most of the observations are made on-axis, meaning that 50% of the flux is lost because of the beam splitter. However, the many K = 9.7 mag CIAO observations are taken off-axis, hence the higher flux. Targets observed with ATs can be as faint as 10 mag. Based on this plot, it is clear that because the flux observed with the UTs is more than 10 times higher, observations will be possible up to K = 13 mag.