Vedic Chronology
The Vedic Chronology is a system of measuring the passage of time by tracking the motion of celestial bodies. It was invented by ancient Indigan scholars in what would become the year 443 VC. The origin point, or year 0, was not the date of the system's creation, but rather the (estimated) birth of Indig, the first of the Indigan emperors.
This system is often used in place of the Imperial Chronology, because it measures time absolutely rather than relative to the life of the current emperor.