Avalonian calendar

The Avalonian calendar was the calendar used by human settlers on the planet Avalon. When settlers from Earth Empire arrived on Avalon in Earth-year 2145 the Avalonian calendar began. When the First Doctor, Susan, Barbara, and Ian visited Avalon in Earth-year 2991, the date on the Avalonian calendar was 846 AL. (PROSE: The Sorcerer's Apprentice)