Comparison between the properties of NGC 3521 and the Milky Way. Panel a: comparison between the radial oxygen abundance distributions. The blue circles denote the T_e-based abundances in individual H II regions in the Milky Way (comes from panel b of Fig. 2), and the solid line is the best fit to those data. The dark triangles mark the R calibration-based abundances in H II regions in NGC 3521. The crimson plus signs are the P calibration-based abundances in H II regions in NGC 3521, and the dotted line is the linear fit to those data points. Panel b: comparison between rotation curves. The points denote the rotation curve of the Milky Way from Eilers et al. (2019). The line shows the rotation curve of the NGC 3521 from de Blok et al. (2008).