- Phase discriminator at Memory Alpha, the Star Trek canon wiki
- Phase discriminator at Memory Beta, the wiki that covers all licensed Star Trek works
Spoilers are precisely defined here. Rules vary by the story's medium. Info from television stories can't be added here until after the top or bottom of the hour, British time, closest to the end credits roll on BBC One. Therefore, fans in the Americas who are sensitive to spoilers should avoid Tardis on Sundays until they've seen the episode.