Representation of a tomographic covariance. In this diagram 3 redshift-bins (1, 2, 3) and 5 COSEBIs modes are assumed to be present. The blow-up shows one of the covariance building blocks; the numbers 1−5 show the COSEBIs mode considered, e.g. 15 means the covariance of E₁ and E₅. The numbers on the sides of the matrix show which combination of redshift bins is considered, e.g., 12 means the covariance of redshift-bins 1 and 2 is relevant. Due to symmetry, only a part of the covariance elements have to be calculated, here shown in pink.