Median spectral residual estimated from the fit of our selection of galaxies with SPARTAN in the VVDS Ultra-Deep survey. We show the relative residual in three redshift bins: 0.5 < z ≤ 0.9 (yellow line), 0.9 < z ≤ 1.9 (purple dashed line), and 1.9 < z ≤ 2.25 (black dot-dashed line). We indicate the number of fits used in the estimation of the residual for each redshift bin. We also show the polynomial fit of the average residual before (orange thick line) and after (blue thick line) spectral correction. The fit is performed on the average of all the redshift bins and enters in the correction of the spectroscopy.