Example of the data reduction procedure. These are the spectra from the first observation night, which are presented in a small wavelength range for demonstration purposes. The spectral matrices from top to bottom are original spectra, normalized spectra, spectra after the first SYSREM, spectra after the second SYSREM, spectra after the Gaussian high-pass filtering, and spectra after the masking. To estimate the efficiency of each data reduction procedure, we computed a metric Q, which is defined as the ratio of the mean value and the standard deviation of each spectral matrix.