use of DBCENTURY

Hi all, I would appreciate some insight into the use of DBCENTURY variable. Do both the tool and the server require to support DBCENTURY, to use its features, or is it sufficient for the server to only have this capability ? What are the values that can be assigned to this environment variable ? I understand that it can be used to change the default century to the century closest, before or after the current date. But what are the respective settings for these ? Thanks in advance, Sandeep