Sky localisation uncertainty as a function of redshift of BNS (white points) detected with ET (left panel) and ET + CE (right panel) over 10 years. Grey points refer to the EM counterparts detectable with Rubin, among which the colored points refer to those that are detectable with WST IFS blue arm at ∼12 hours post-merger. Different colors correspond to different S/N. Percentage reported in the legend refer to the fraction of EM counterparts that are detectable with WST, with respect to those that are detectable with Rubin. The black dashed line represents WST patrol area, 3.1 deg², where fibres will be positioned.