a factor of three[^2].

The separation of the chemical and structural part, dictated by computational efficiency, however has the consequence that, during the solution of the physical structure, any additional mixing which is related to the movement of the boundary of the convective zone is not taken into account. Hence, when the upper boundary of the HECZ moves outward, the program treats hydrogen burning for the current position only, yielding smaller energies than when additional hydrogen is mixed down into hotter regions from layers just becoming convectively unstable.

If the time step during this phase is chosen too large, all protons will be captured completely in the computation of the chemical evolution. The energy released, however, will be that of the total (and larger) time step. The specific energy release per second is therefore lower than it actually would be if the additional mixing due to the advance of the convective boundary had been included. With very short time-steps one could better follow the movement of the convective zone and thus changes in the hydrogen luminosity. However, experience shows that the (numerically) still discontinuous penetration of the HECZ into H-rich layers leads to oscillations in the hydrogen luminosities, and the 