These files are compress tar files.  There is one file per month.  To
unpack a file, you need to uncompress the file and then untar it.  If
you have the 'zcat' utility you can do something like:

	zcat apr_94.tz | tar xvf -

The digests will be in a directory with the same name as the base of
the file name (apr_94 in the example shown above).

Ralph