Time trend of the median S/N for each transit observation of KELT-9 b as a function of orbital phase. The HARPS-N S/N values have been scaled to values that would be expected to be produced for the exposure times taken by the FOCES spectrograph. The HARPS-N transit covers the transit of the entire planet, and a substantial amount of the baseline. Additionally, the S/N is consistently higher throughout the entire observation compared to the observations taken by FOCES. Signal quality also drops off for all the FOCES nights towards the end of each night.