"Of the events that have transpired over the last year, there are many rumors and far fewer facts. Those rumors could all be dispelled by having an exact chronology of events created, and perhaps, in another generation or two, such a chronology could be made public. While we were a covert force fighting against the Empire, there was no questioning the need for stealth and secrecy. It was what kept us alive and allowed us to fight on against the Empire. Because of this secrecy we have defeated them in battle after battle."
―New Republic Chief of State Mon Mothma, following Ysanne Isard's final flight from Coruscant[src]
↑The New Essential Chronology states that the Ruusan Reformation occurred in 1000 BBY, which is the zero point of the calendar based on the Ruusan Reformation, so the difference between the calendar based on the Battle of Yavin and the Ruusan Reformation's year-notation system is 1,000 years. This date is derived using simple math based upon other confirmed dates.