What ACIS gain file was used in the automatic processing?
The name of the gain file used in processing can be found in the header of the level 1 event file for grating observations and of both the level 1 or level 2 for imaging observations:
unix% dmkeypar acisf01843N001_evt2.fits gainfile echo+ /data/CALDB/data/chandra/acis/bcf/gain/acisD2000-01-29gainN0001.fits