70459501 2019 352 00:00 2 6 APD realignment. Better center pupil image on APD.  Resulted in better timing performance. 
70459501 2019 233 00:00 2 6 Switch 40 micron APD for best-available 30 micron.  Systematic characterization of APD timing performance as function of breakdown voltage and discriminator thresholds was done to determine best performer. 
70459501 2018 131 00:00 2 9 Cesium clock is now, again, APOLLO timebase. 
70459501 2017 355 00:00 2 9 XL-DC again is APOLLO timebase.  Cesium clock experienced multiple fatal errors, was shipped off for repair. 
70459501 2017 046 00:00 2 9 Cesium clock is now, again, APOLLO timebase. 
70459501 2017 034 00:00 2 9 XL-DC again is APOLLO timebase.  Reverted to previous hardware state for diagnosing problem with APOLLO system. 
70459501 2017 004 00:00 2 9 Cesium clock is now APOLLO timebase. 
70459501 2016 043 00:00 1 9 Began universal counter (UC) clock frequency comparison between cesium and XL-DC. XL-DC still timebase for APOLLO.   
70459501 2013 250 00:00 0 6 APD readout electronics/motherboard changed. Same APD. 
70459501 2012 098 00:00 2 6 Began using different gate width.  Improved data quality. 
70459501 2010 311 00:00 2 6 Switch from 30 micron APD to 40 micron