Oracle: Timestamp

Here's something new, i got earlier.
DECLARE
systime TIMESTAMP;
total interval day(6) to second(6);
BEGIN
systime := SYSTIMESTAMP;
Dbms_Output.put_line('Initial time:' || systime);
sys.dbms_lock.sleep(10);
SELECT SYSTIMESTAMP - systime INTO total FROM dual;
Dbms_Output.put_line('Period:' || total);
END;
/

Sorry! no explaination. ;-)