Relative errors in the equal redshift angular power spectrum for redshift bin 1, 4, 8, and 13 of Euclid, using 13 equi-populated bins (DR3). We show the full calculation result from CLASS as a black solid line, and the Limber approximation result as a purple dashed line. The green dashed line corresponds to the recalibrated version of the flat-sky approximation. The relative error associated with the Gaussian covariance calculated at 1σ for the given survey configuration is shown as the grey contour. We note that the y-axis ranges are [ − 50, 50], in contrast to Figs. 2 and 3.