The results of CAL pedestals calibration in LEX8 and HEX8 ranges for the first 44 runs collected on orbit showed a significant bias with respect to the pedestals actually used for the data processing in the pipeline (they were measured during cold thermal balance period of Observatory TVAC in January 2008).
The plot below shows the pedestal trending the trending of pedestal difference with respect to official pre-launch pedestal file for all LEX8 channels over 44 runs:
Similar plot for all HEX8 channels:
The reason for this pedestal drift is that temperature on orbit with respect to cold_TVAC - pedestals for the first 12 runs demonstrate some evolution, while CAL temperature was increasing and after that became stable. The maximum pedestal drift is 30 adc units, which corresponds to 1 MeV in LEX8 range and 60 MeV in HEX8 range.