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Details of the Calendar Package

Conventions for Numbering Years

 • There are two commonly used year naming conventions in use. The first is the "Dionysian convention," or the Common Era notation system.
 • Dionysius Exiguus created the scheme for numbering using as a reference point his calculation of the year in which Jesus Christ was born (the year AD 1).
 • Since the number $0$ was not yet known at the time this system was devised in sixth century Europe, the previous year was named 1 BC. This system, while still very widely used in a slightly more modern form employing the religiously neutral "CE" ("Common Era") and "BCE" ("Before the Common Era") suffers from the lack of a year 0, which makes date arithmetic inconvenient.
 • The astronomer Jacques Cassini proposed, after the introduction of negative numbers, what is now called the "Cassini convention." The year 1 BC in the Dionysian convention is year 0 in the Cassini convention, and years prior to that are given negative numbers. Thus, for example, 47 BCE is the year -46 in the Cassini convention. In general, the year $Y$ BCE is the year $1-Y$ in the Cassini convention. The Cassini convention is universally used in scientific calculations today, while the Dionysian convention is commonly used by historians.
 • Maple's Calendar package uses the Cassini convention exclusively for numerical input and output of years.