Two comparable standard calibration units exist and can be internally exchanged if needed. One unit serves all standard telescope foci while the other serves just the Fabry-Pérot unit on the optical bench of the spectrograph. Each unit contains three halogen lamps (two hot spares) and two Th-Ar lamps (one hot spare). We employ flat-field halogen lamps with four fibre exits and Th-Ar lamps with single fibre exits. The halogen sources are tunable 100 W lamps from LOT-Oriel. The Th-Ar lamps are from Photron and Juniper.
Beside the standard wavelength calibration, PEPSI radial velocities can be obtained relative to a Fabry-Pérot etalon. The etalon fringes are imaged simultaneously with the target spectrum. On average more than hundred fringes are available per echelle order.