4.  The amount of time between two dates.

      $date1=&ParseDate($string1);
      $date2=&ParseDate($string2);
      $delta=&DateCalc($date1,$date2,\$err);
          => 0:0:WK:DD:HH:MM:SS   the weeks, days, hours, minutes,
                                  and seconds between the two
      $delta=&DateCalc($date1,$date2,\$err,1);
          => YY:MM:WK:DD:HH:MM:SS  the years, months, etc. between
                                   the two