A four-crystal monochromator beamline will be part of the radiometry laboratory that the Physikalisch-Technische Bundesanstalt will install at the new storage ring BESSY II. The most important design criteria for the beamline are the tunability of the photon energy in a wide spectral range from 1.75 to 10 keV, the high spectral purity of the radiation, as well as the good reproducibility of the absolute photon flux.