Relation between Δlog(SFR) and the iso-D_n(4000) ranges. The symbols are colour-coded depending on the D_n(4000) range and according to Fig. 2, being D_n(4000) < 1.1 (blue), 1.1 ≤ D_n(4000) < 1.2 (green), 1.2 ≤ D_n(4000) < 1.3 (red), 1.3 ≤ D_n(4000) < 1.4 (cyan), and 1.4 ≤ D_n(4000) < 1.5 (magenta). The symbol type is related to the log(M_⋆/M_⊙) range considered, as labelled. For the stellar mass range 8.5–9.0 (circles), only a lower limit, if any, for Δlog(SFR) could be assumed from the present SDSS sample, leading to log(SFR) < −1.5. In the case of the iso-D_n(4000) line 1.2 ≤ D_n(4000) < 1.3, the value of the intersect position has been derived by slightly extrapolating this iso-D_n(4000). The mean value of Δlog(SFR) for each iso-D_n(4000), considering all the iso-masses, is shown by the coloured numbers (only lower limits of Δlog(SFR) for the 8.5 ≤ log(M_⋆/M_⊙) < 9.0 mass range are not considered). The black dotted line indicates Δlog(SFR) = 0.