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                                    NUSTAR
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NuSTARDAS V1.9.1 and V1.9.2:

 numetrology:

 This NuSTARDAS release is required for analysis of all NuSTAR
 observations performed after March 16, 2020. On that date the on-board
 metrology system (which tracks the relative motion of the NuSTAR optics
 bench and the focal plane bench) underwent a flight software upgrade to
 improve the longevity of the metrology laser system.

 NuSTARDAS V1.9.1 and V1.9.2 are upgrades to handle metrology data in
 METSTATE 4 and 6, respectively, which are flags in the data stream that
 self-document the state of the laser metrology system. These software
 changes are transparent to the user requiring no syntax changes when
 calling Stage 1 of nupipeline. There is no change to the quality of the
 science data.

 Please note that attempting to use NuSTARDAS V1.9.0 (released with
 HEASoft 6.27) or any earlier versions of the NuSTARDAS with data taken
 after March 16, 2020 will result in an error during Stage 1 of the
 pipeline processing and result in empty PSD, corrected PSD, and mast
 files.

 This version of NuSTARDAS is backward compatible with all NuSTAR data
 in the HEASARC from before March 16, 2020.

 More details can be found in the NuSTAR Software Users's Guide.