Illustration of the convergence properties of plasma and radiation field quantities. We show the fractional changes between successive iterations for the mean intensity of the radiation field J, the electron temperature T_e and a representative level population, specifically that of the second excited level of hydrogen n₃. In all cases, we include both the changes in each individual shell (gray) as well as their average (blue). The results shown here are taken from our SN1999em model for the 14th of November (see Sect. 4 and Fig. 3).