Warnings related to missing SUM_2X2, OCLKPAIR, FEP_CCD, or ORC_MODE keywords
Users trying to run this tool with old versions of data products, those created with ASCDSVER less than version 8.4.2, may see warnings like
FITSIO status = 202: keyword not found in header *** ERROR: *** Unable to get the value of `SUM_2X2' in /data/acisf04425_000N003_evt1.fits
Users should reprocess their data or use the r4_header_update script.