Time safe

The time safe was a feature found in various TARDISes, commonly stored behind a roundel in the console room.

A time safe was used to provide a Time Lord with something from the future that would be needed at that point in the TARDIS's relative past. The Fifth Doctor described it as a permitted temporal paradox that must be used sparingly.

The Doctor used it to send himself the diary of Captain Richard Haliwell regarding the British expedition to the Moon in 1878, alerting him and Turlough to their role in the expedition. (PROSE: Imperial Moon)