Calendar

A calendar was a dating system used by humans. For many centuries, Earth used the Gregorian calendar. (PROSE: Instead of You) Other human-occupied planets, such as Avalon, used their own calendars. (PROSE: The Sorcerer's Apprentice)

The Tenth Doctor cited calendars as an example of how humans made sense out of chaos. (TV: The Runaway Bride)

Towards the end of the 22nd century Dalek invasion, the First Doctor and Ian Chesterton found a discarded calendar which gave the year as 2164. (TV: The Dalek Invasion of Earth)

The First Doctor and his companions, Ben Jackson and Polly Wright found out that they were in December 1986 when they saw a calendar at Snowcap. (TV: The Tenth Planet)