Automatic Hickey-Frieden absolute cavity radiometer. This is themodel designation given by The Eppley Laboratory, Inc. for theircommercial version of an electrically self-calibrating absolute cavityradiometer used to define and transfer the World Radiometric Reference(WRR) to pyrheliometers and pyranometersused for solar irradiancemeasurements. The WRR is maintained at theWorld Radiation Center, Davos,Switzerland for theWorld Meteorological Organization.