Total transmission of the spectra’s first order (solid line) and ten times total transmission of the spectra’s zeroth order (dashed line) for the BGS000 (blue), RGS000 (light red), RGS180 (orange), and RGS270 (dark red) grism channels. The total transmission accounts for the transmission of the grisms themselves, of CoLA and CaLA, and includes the detector quantum efficiency. For comparison, the Fabry–Pérot etalon spectrum (light grey) is shown as measured in the laboratory with a Lambda 900 spectrometer, in arbitrary data units. The contributions from neither the dichroic nor telescope are accounted for in these measurements as Euclid mirrors as well as its dichroic were not emulated during the instrument tests.