Example of a synthetic pseudo-spectrum as typically provided by the OTELO survey. Top panel: flat continuum (thick line) with Hα+[NII]6549,6584 Å emission lines as Gaussian profiles (FWHM = 6 Å). A log₁₀([NII]6584Å/Hα) = −0.3 ratio was chosen for this example. The observed Hα and [NII]6584Å EWs are 15.5 and 7.7 Å respectively. Poissonian noise was added to this spectrum (thin line) and then convolved with the transmission curves represented in Fig. 2 to mimic the OTELO survey scan. The result is shown in the bottom panel. Flux errors were computed by propagation, taking into account the continuum deviation at the input spectrum multiplied by the minimum pixel area, and the nominal readout noise. The dashed line represents 2σ_c deviations above the fitted pseudo-continuum.