The evolutionary track of abundance ratios as predicted by the models of Legrand (2000). A mild continuous SF with ϵ = 0.001 Gyr^-1 is shown by solid black lines, whereas a mild continuous SF (ϵ = 0.001 Gyr^-1) combined with a current burst (SFR = 0.023 M_⊙ yr^-1, i.e., ϵ = 0.88 Gyr^-1 if M_HI = 2.6 × 10⁷ M_⊙, during the last 20 Myr) is shown in dashed red lines. The blue shade areas show the continuous SF with 1.45 × 10^-3 ≤ ϵ ≤ 3.85 × 10^-3 Gyr^-1 which is derived from the observed SFR and M_HI data of IZw 18 (see Table 1 of Legrand 2000). Cyan open circles are BCDs and open green squares are DLAs, as in Fig. 3.