Wavelength calibration accuracy evaluated on a sample of QSOs with emission lines in their spectra. Top panel: difference in AL sample position of emission line peaks measured on BP and RP mean spectra and the expected position measured on simulated mean spectra (filled symbols). Open symbols refer to SEDs with incomplete wavelength coverage for which the expected position has been estimated based on the line wavelength at rest and the QSO redshift value. The vertical grey line separates BP from RP data. The black lines delimit the region within ±10% FWHM of the LSF for mean spectra. Bottom panel: observed and expected emission line wavelengths as measured on the ECS. Dashed grey lines represents ±10% of the expected LSF FWHM for calibrated spectra, and black lines delimit the region within ±10% FWHM of the LSF for mean spectra.