Ommin: "How goes the battle in the city above us?"
Novar: "Not well, King Ommin. For the first two days, we drove the enemy back. But the Republic has arrived. And another Jedi, a female! They seemed to have evened the scales! Our Sith magic no longer controls ebb and flow!"
Ommin: "All because of one new Jedi? Her power must be great! Hmm. I shall have to deal with her immediately."
↑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.