The files tha_fgmcal.txt, thb_fgmcal.txt, thc_fgmcal.txt,
thd_fgmcal.txt and the_fgmcal.txt contain time depenndent calibration
parameters for the FGM instrument on each THEMIS probe. Each row of
each file contains a time followed by 13 values. The first 3 values
are offsets, the next 9 are a 3 by 3 matrix of gain factors, followed
by the nominal spin period. These files are updated regularly. For
details on the calibration process, see the document:
ftp://apollo.ssl.berkeley.edu/pub/THEMIS/3%20Ground%20Systems/3.2%20Science%20Operations/Science%20Operations%20Documents/thm_soc_113_FGM_CALPROC_20061018.pdf.