TUNED_UNDORETENTION is zero

 Hello Expert,

Can we check why TUNED_UNDORETENTION is 0..? 

SQL> select banner from v$version;

BANNER

----------------------------------------------------------------

Oracle Database 10g Enterprise Edition Release 10.2.0.4.0 - 64bi

PL/SQL Release 10.2.0.4.0 - Production

CORE    10.2.0.4.0      Production

TNS for Solaris: Version 10.2.0.4.0 - Production

NLSRTL Version 10.2.0.4.0 - Production

SQL> show parameter statistics_level

NAME                                 TYPE        VALUE

------------------------------------ ----------- ------------------------------

statistics_level                     string      TYPICAL

SQL> select begin_time,ssolderrcnt from v$undostat;

BEGIN_TIME          SSOLDERRCNT

------------------- -----------

2012-06-01 19:02:14          78

SQL>  select BEGIN_TIME,END_TIME , TUNED_UNDORETENTION from v$undostat;

BEGIN_TIME          END_TIME            TUNED_UNDORETENTION

------------------- ------------------- -------------------

2012-06-01 19:02:14 2012-11-09 03:59:20                   0

SQL> select begin_time,maxquerylen from v$undostat;