Behaviour of U (cf. Eq. (A.13)), in three models with M = 1 M_⊙, R = 7 R_⊙. The dotted curve shows the original YREC model, the pluses marking the mesh points in the evolution calculation. The solid line shows the same model, after application of the correction procedure discussed in the text. For comparison, the dashed curve shows the corresponding ASTEC model, for which no correction had to be applied. The thin dot-dashed line marks U = 3.