Examples of high-resolution spectra for various calibrating classical Cepheids collected with the spectrographs HARPS, UVES, FEROS, and STELLA. The vertical lines indicate the position either of iron lines only used for the metallicity determination (dashed) or of lines also adopted in the LDR method (solid). The name of the Cepheid, its mean metallicity, phase, and S/N of these example spectra around 6000 Å are also labeled.