known_biases: air-fluorescence calorimetric energy reconstruction shares a common ~20-30% absolute energy-scale systematic (fluorescence yield, atmospheric/aerosol attenuation, missing-energy correction, detector calibration); an error here shifts every Fly’s Eye energy (spectrum normalisation and the single Oh-My-God event) together. Duty cycle limited to clear moonless nights. Basis for S-43 and S-46.