Year zero
Year zero does not exist in the anno Domini system usually used to number years in the Gregorian calendar and in its predecessor, the Julian calendar. In this system, the year is followed by . However, there is a year zero in astronomical year numbering (where it coincides with the Julian year ) and in ISO 8601:2004 (where it coincides with the Gregorian year ) as well as in all Buddhist and Hindu calendars.
Library of Congress Control Number
In its most elementary form the number includes a year and a serial number. The year has two digits for 1898 to 2000, and four digits beginning in 2001. The three ambiguous years (1898, 1899, and 1900) are distinguished by the size of the serial number. There are also some peculiarities in numbers beginning with a "7" because of an unsuccessful experiment applied between 1969 and 1972.