Comparison between the effective oxygen yields in the NGC 3521 and the Milky Way for the radial oxygen abundance distributions shown in Fig. 9 and the gas mass fraction distributions displied in Fig. 11. Panel a: The circles denote the effective oxygen yields in NGC 3521 as a function of radius and the bars show their uncertainties. The plus signs designate the radial distribution of the effective oxygen yields in the Milky Way based on the Σ_⋆ with the stellar disc scale length of h_d = 2.6 kpc and on the Σ_gas from McMillan (2017); the points are the yields based on the Σ_gas from Söding et al. (2024). The square marks the effective oxygen yield in the solar vicinity based on the Σ_gas from McKee et al. (2015). The lines show the upper and lower values of the empirical estimations of the oxygen yield. Panel b: Same as panel (a), but for the stellar disc scale length of h_d = 3.1 kpc.