Gaia-ESO Survey stars in a typical young open cluster. This presents a single Giraffe setup of about 100 stars with spectra scaled to illustrate the dynamic range, and sorted in temperature (hottest at the top). The top panel is Giraffe HR9B, 514–535 nm, the lower HR15N, 644–682 nm. This illustrates the wide range of astrophysical parameters, and hence appearances of the spectrum, which must be managed in a wide-ranging stellar survey.