Measured galaxy power spectrum multipoles calculated from dedicated mocks (Pezzotta et al. in prep.) based on the Flagship simulation (see Sect. 6.1) of the Euclid emission-line sample for a redshift bin 1.3 < z < 1.5, compared to a best-fit model based on effective field theory (EFT, also called EFTofLSS, see Sect. 8.2.2 for further discussion) assuming k_max = 0.25 h Mpc⁻¹. Error bars here correspond to the Euclid full mission volume for this redshift bin prior to observational effects.