There is, for example, the One True Discordian Calendar , which is naturally superior to all others. His ideas are also naturally superior to all others, but Robert Anton Wilson is a nincompoop, and a bald-headed liar besides. Therefore, we reject his system, even if it isn't really a system at all, which it is. In any case, his essay describes many and varied year-numbering systems, so we won't repeat them here. There are certainly many more, too.
Humans have an obsession with round numbers .
This leads people to attach importance to otherwise unimportant units of time larger than the year itself, which is nicely based on the Newtonian mechanics of the solar system and therefore has some basis in observable phenomena. Most notably, this penchant for round numbers causes people to regard human history in terms of decades , starting with years that end in one zero, and centuries , starting with years that end in double zeroes. Consider that sometimes, chaos can appear very orderly, and that, even in a chaotic system, certain disorderly elements may get their ass kicked regardless. It occured to this author, thinking about human life spans, that the division of human time into centuries is an unfair and arbitrary split. But, when one looks at dates in terms of decades and centuries, that's the idea one gets.