# 6.4.2 Calibration preparation

This step is in charge of preparing the spectra for the Calibration workflow: to select the calibrators, and to clean their spectra.

The wavelength calibration module needs high S/N spectra presenting deep absorption lines. Therefore the calibrators are selected based on their magnitude (external $G_{\rm RVS}$ $<9$ mag) and on their atmospheric parameters ($4500<$ $T_{\rm eff}$ $<6500$ K). Figure 6.4 shows an example of a wavelength calibration star spectrum.