Release 20170720 Summary of changes: CLOCK: NuSTAR clock correction file, version 73, is available. This file is up to date through 2017-07-20, compared to 2017-06-14 in the previous version (72). The latest clock file is available from the SOC public website: http://www.srl.caltech.edu/NuSTAR_Public/NuSTAROperationSite/clockfile.php IMPORTANT NOTE - The versions of clock correction files v022 to v063 were found to have unphysical discontinuities in the clock correction. Only versions v066 and later should be used in analysis.