The Xi’an calendar (Modern Xi’an Year, r.aiXy’an) is measured by the celestial mechanics of their former homeworld, RyiXy’an (Hyoton III). It differs from the Human calendar in a number of significant ways; for example, each Xi’an year is equivalent to 1.28 Human years, is assigned a number counting upwards from when the current Imperial House ascended to the throne, and is prepended with a number that represents the corresponding Imperial Age. The First Imperial Age began in the Human year 19668 BCE, and was recorded by the Xi’an as I.0 (or 1.0) The current Third Imperial Age began in the Human year 1457, and was recorded by the Xi’an as as III.0 (or 3.0).