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But for calibration unit the correction proposed by Philippe could be applied and should be implemented in reconstruction.   

 Nonlinearity in HEX8 vs LEX1 correlation in ADC units

    To study nonlinearity down to low energies ~10 MeV comparable to HEX8 noise it is necessary to properly average this noise. This is possible when using ADC units rather than reconstructed energy (or DAC values) because ADC values below pedestal are kept. The folowing plot shows 2d histogram of  HEX8 vs LEX1 adc signals for all crystal ends and all events of one on-orbit nomSciOps run (244425100), the only selection is gemDeltaEventTime > 100 us.