Yearometer

The yearometer was an instrument in the Doctor's TARDIS that showed the TARDIS' position in time and space. It stopped calculating properly after the First Doctor left 1963 England. (TV: "The Cave of Skulls")

When the TARDIS arrived at Byzantium, the yearometer gave the date as 14 March 64. (PROSE: Byzantium!)

When the TARDIS arrived at Marpling, the yearometer gave the date as 27 August 1933, though Anji Kapoor was incredulous that it was named this. (PROSE: Eater of Wasps)