The observed energy spectrum for elastic ep events had a mean at around 2.36 GeV for run 68606. The corresponding spectrum for run 68618 has a mean for around 2.28 GeV. See plot below (red is 68606, black is 68618).
This drop in mean energy over a period of 5 hours is around 4 %.
We will investigate the possibility of recalibrating BigCal HV levels and discriminator thresholds.
Figure 1
