Astronomical year numbering
Cassini gave the following reasons for using a year 0:
Fred Espanak of NASA lists 50 phases of the moon within year 0, showing that it is a full year, not an instant in time. Jean Meeus gives the following explanation:
Although he used the usual French terms "avant J.-C." (before Jesus Christ) and "après J.-C." (after Jesus Christ) to label years elsewhere in his book, the Byzantine historian Venance Grumel used negative years (identified by a minus sign, −) to label BC years and unsigned positive years to label AD years in a table. He did so possibly to save space and put no year 0 between them.
Vehicle identification number
The year 1980 was encoded by some manufacturers, especially General Motors and Chrysler, as "A" (since the 17-digit VIN was not mandatory until 1981, and the "A" or zero was in the manufacturer's pre-1981 placement in the VIN), yet Ford and AMC still used a zero for 1980. Subsequent years increment through the allowed letters, so that "Y" represents the year 2000. 2001 to 2009 are encoded as the digits 1 to 9, and subsequent years are encoded as "A", "B", "C", etc.