Aztec calendar
From Tardis Wiki, the free Doctor Who reference
The Aztec calendar was a human dating system to which the Sixth Doctor sarcastically referred when Peri asked for the date in "human terms" when they arrived in 3174. He informed her that the day was "nine-Ehecatl day" according to the Aztecs — "but that‘s hardly either here or there after all that unfortunate business with Cortez". (PROSE: Burning Heart)
