Measurement of the Flux of Ultrahigh Energy Cosmic Rays from Monocular   Observations by the High Resolution Fly's Eye Experiment
  We have measured the cosmic ray spectrum above 10^17.2 eV using the two air fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, photo-tube and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extra-galactic sources. 
The High Resolution Fly's Eye Collaboration