Results of the EWS simulation comparing the extracted versus incident fluxes of the Fto-complex (left), [O III]λ5008 (middle) and [S III]λ9531 (right) emission lines. The scattered circles are corrected for the estimated loss due to the aperture (see Sect. 5.1.3). The sources are colour-coded with the S/N of the emission line measurement, as shown by the right-side colour bar. The grey circles are objects with S/N < 3.5. The black diagonal line shows the 1:1 ratio. The grey dotted lines are the requirements for the Euclid spectroscopic detection limit for the EDS (leftmost) and EWS (rightmost) surveys. The contours correspond to iso-proportions of the distribution density of our measurements, starting at 20% with a 10% step, before applying the correction due to the aperture loss.