18 was a number.

When Charles Winlett was infected by the Krynoid, his pulse rate lowered to eighteen a minute. (TV: The Seeds of Doom)

In what the Tenth Doctor termed "a little leeway", the Master could only have taken the Doctor's TARDIS to as far back as eighteen months prior to its last departure in May 2008. Indeed, the regenerated Master made his first appearance on Earth, under the alias of "Harold Saxon", just after the downfall of Harriet Jones on Christmas 2006. (TV: The Sound of Drums)

Community content is available under CC-BY-SA unless otherwise noted.