Real-time display of a raw spectrum. A small portion of a star + Fabry-Pérot spectrum acquired in the 4-UT configuration is shown. The main dispersion is vertical. Each order consists of two spectral traces (slices) of the Fabry-Pérot, with its characteristic equidistant spectral lines, and two traces of the stellar spectrum, which essentially plots the continuum with a few absorption features. This figure is best understood when tilted by 90° and compared to Fig. 4.