The Hooman Calendar
The Hooman calendar is split into three ages, intended to mirror the development of their nation. The ages are as follows: E.S. referring to the times of Early Settlement, O.R. denoting the Owl Republic, and N.S. being the current days of a New Start.
One curious aspect of this system is that E.S. progresses backward. To give an example: The first Hoomans settled in what would become the port city of Avisporte in E.S. 152, but the first recorded maritime contact between an Avisporte ship and a v-tail orca took place in E.S. 36.
There is also no year 0 in any of the three ages. It goes directly from E.S. 1 to O.R. 1. There was some deliberation of whether to make the final year of O.R. also the zeroth year of N.S., but it was ultimately decided against to reduce possible confusion in bookkeeping.
Lastly, although the Hooman calendar uses the same system as a whole with most/all other Holo nations, one point where it differs is when each age officially begins. The end of E.S. and beginning of O.R. are with the signing of the Proclamation of Unification, generally seen as the beginning of the Owl Republic as a unified nation-state. N.S. 1 began with The Nameless One's Cessation of Divinity, as /who/ puts it. This resulted in O.R. starting in late summer and N.S. beginning mid-spring. This, combined with /who/'s decentralized nature, has made it difficult for them to establish formal ties with other nations.