oracle compression?

test.sql

CREATE TABLE tstc (value varchar2(4000)) COMPRESS;

INSERT INTO tstc (value)
SELECT substr(rpad(to_char(LEVEL), 3999, to_char(LEVEL)), 0, 4000)
FROM dual
CONNECT BY LEVEL <= 1000*1000;


select segment_name,segment_type, sum(bytes/1024/1024/1024) GB
 from dba_segments
 where segment_name='TSTC' 
group by segment_name,segment_type;

SEGMENT_NAME|SEGMENT_TYPE|GB          |
------------+------------+------------+
TSTC        |TABLE       |3.8564453125|