Variations of luminosity during the RGB bump for the 0.8 M_⊙ model with Y_ini = 0.248. The luminosity starts dropping when the H-burning shell encounters the H-abundance discontinuity left behind by the convective envelope during the first dredge-up; it increases again when this discontinuity has been crossed. In Table 2 we give the time the star spends between the lower and upper horizontal lines, as well as the luminosity of the bump indicated by the middle horizontal line.