Top four panels – Difference in atmospheric parameters between the current analysis and da Silva et al. (2022) as a function of pulsation phase for the calibrating Cepheid ζ Gem. Dark symbols indicate STELLA spectra, whereas orange symbols mark HARPS spectra. Black solid lines display zero difference. Bottom four panels – same as the top four panels, but the difference is between NLTE and LTE estimates of the atmospheric parameters. Light blue symbols indicate STELLA spectra, whereas red symbols mark HARPS spectra.