Stellar metallicity measured for our sample of 20 calibrating Cepheids compared with results from literature. Top panel: metallicity as a function of the Galactocentric distance from the current work (blue circles) and from literature (gray circles): Luck et al. (2011, LII); Luck & Lambert (2011, LIII); Lemasle et al. (2013, LEM); Yong et al. (2006, YON). A linear regression (solid black line plus equation) fitted to the entire sample is compared with the radial gradient provided by Ripepi et al. (2022) (dashed magenta line). The latter was artificially shifted to coincide with the current radial gradient at R_G = 10 kpc. The R_G values are from Genovali et al. (2014). Bottom panel: Same as the top, but as a function of the logarithmic pulsation period. A linear regression (solid blue line plus equation) fitted to the current sample is also shown.