The files psef_calib_params.txt and psif_calib_params.txt in this
directory contain parameters used in the calibration of THEMIS SST
Level 1 data, for electrons and ions, respectively.  The files are autogenerated by an IDL program distributed with the THEMIS Data analysis software.  The program is themis/spacecraft/particles/SST/SST_cal_workdir/thm_sst_cal_files.pro

Details regarding SST & calibration can be found in the
document:
ftp://apollo.ssl.berkeley.edu/pub/THEMIS/3%20Ground%20Systems/3.2%20Science%20Operations/Science%20Operations%20Documents/thm_sst_davin_larson_June2009.pdf