The exact behaviour if the 4 different modes is,
DISABLED - No changes are made to the history by
any ASTERIX application
QUIET - Only program version ids, time and cpu
stamps are written
NORMAL - Normal level of history update.
Applications attempt to write all
information required to recreate output
VERBOSE - Same as NORMAL for ASTERIX applications,
but other Starlink s/w may perform a
higher level of update than NORMAL.