*tracks*
    Can be one or more ASCII, native binary, or COARDS netCDF 1-D data
    files. To supply the data files via a text file with a list of
    tracks (one per record), specify the name of the track list after a
    leading equal-sign (e.g., =tracks.lis). If the names are missing
    their file extension we will append the suffix specified for this
    *TAG*. Track files will be searched for first in the current
    directory and second in all directories listed in
    **$X2SYS\_HOME**/*TAG*/*TAG*\ \_paths.txt (if it exists). [If
    **$X2SYS\_HOME** is not set it will default to
    **$GMT\_SHAREDIR**/x2sys]. (Note: MGD77 files will also be looked
    for via **MGD77\_HOME**/mgd77\_paths.txt and \*.gmt files will be
    searched for via **$GMT\_SHAREDIR**/mgg/gmtfile\_paths).
