Comparison lamps for the IDS are mounted in the INT Cassegrain A&G box, which is described in more detail in Section . Three lamps can be fitted, one of which is always the tungsten lamp, used as a white light source. The standard set-up is a tungsten lamp, copper-argon and copper-neon discharge lamps for wavelength calibration. The following discharge lamps are also offered: Deuterium, Th-Ar, Fe-Ne, Fe-Ar, Al/Ca/Mg-Ne, Na/K-Ne, Cu-He, and He. Arc maps are available for the Cu-Ar, Cu-Ne, Th-Ar, He and Al/Ca/Mg-Neon (La Palma Technical Note 70).