After Foundation

From Tardis Wiki, the free Doctor Who reference

After Foundation - often shortened to AF - was the dating system used in the City of the Saved. It measured how many Earth years had passed since the foundation of the City, with the first year of the City's existence being AF 0. (PROSE: The Book of the War, Of the City of the Saved...)

The final year in this dating system was AF 300, the year in which the City was destroyed. (PROSE: Apocalypse Day)