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The following plot show the time evolution of peak positions for B, C, N and O peaks:
All four peaks show linear decrease with very close relative slope:
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I've done the proton calibration of individual crystals for the same time periods and compared the results with the initial on-orbit calibration done on June 28, 2008 and used of reconstruction so far.
The results are shown on the following plot: 
Each histogram shows the histogram of ratios of calibration coeffient of each crystal at some time period to its initial value on June 28, 2008.
Last plot shows the evolution of the mean value of the histograms and has the linear decrease of 1.35+-0.02% per year, consistent with the slope determined form GCR peaks.
We have to correct this calibration change by using new calibration made recently and by recalibrating the CAL every 6 month.
To correct the data already processed possible solution is to introduce energy correction to reconstructed energies linear with time.