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In reality the influence of this bias in ground calibration is even more significant, because for segments 0 and 11, which cannot be calibrated directly (because of spread caused by the effect of direct light) the calibration constant was linearly extrapolated from segments 1 and 10 and the bias of 4 mm become 8 mm in segments 0 and 11.
The error mentioned above was the biggest, but not the only source of systematic errors in asymmetry calibration. When I compared the calibrations based on data collected in August 2008 and in October 2009, the difference shows systematic behaviour with position along the crystal:
(C&A 21 June please look at the following section second)
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