To process two-digit years in the year 2000 and beyond, the date and time callable services use a sliding scheme in which all two-digit years are assumed to lie within a 100-year interval (the century window) that starts 80 years before the current system date.
In the year 2008 for example, the 100 years that span from 1928 to 2027 are the default century window for the date and time callable services. In 2008, years 28 through 99 are recognized as 1928-1999, and years 00 through 27 are recognized as 2000-2027.

By year 2080, all two-digit years will be recognized as 20nn. In 2081, 00 will be recognized as year 2100.
Some applications might need to set up a different 100-year interval. For example, banks often deal with 30-year bonds, which could be due 01/31/28. The two-digit year 28 would be interpreted as 1928 if the century window described above were in effect. The CEESCEN callable service lets you change the century window. A companion service, CEEQCEN, queries the current century window.
You can use CEEQCEN and CEESCEN, for example, to cause a subroutine to use a different interval for date processing than that used by its parent routine. Before returning, the subroutine should reset the interval to its previous value.