Time safe

The time safe is a feature found in various TARDISes.

A time safe is used to provide a Time Lord with something from the future that will be needed at that point in the TARDIS's relative past. The 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 Halliwell regarding the British expedition to the Moon in 1878, alerting him and Turlough to their role in the expedition (PROSE: Imperial Moon).