Isomorphic controls

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Isomorphic controls could only be operated by one user. Such controls ostensibly worked only after identifying the allowed user through genetics or other uniquely identifying properties, such as their biological morphic field, of which the name "isomorphic" was derived from.

One such device was the Saxon Master's laser screwdriver. The Tenth Doctor attempted to use it to overpower the Master, only to be ridiculed when he could not. (TV: Last of the Time Lords)

The TARDIS' controls were said to be flatly isomorphic, (TV: Pyramids of Mars) or at least uniquely operable by the Doctor. (TV: "The Rescue") This fact prevented a shape thief from stealing the TARDIS, even though he had perfectly mimicked the first incarnation of the Doctor. (AUDIO: Mother Russia) However, Sekhmet described isomorphic controls as "a transparent lie, fit only to deceive a child," i.e. a bluff. The Fifth Doctor seemed to agree with this sentiment by simply stating, "Oh, it worked before." (AUDIO: The Bride of Peladon) Indeed, there were several instances of companions (and non-companions) successfully using — or even being actively taught to use — the TARDIS controls. (TV: The Pirate Planet, Castrovalva, Four to Doomsday, Utopia, The Sontaran Stratagem, Journey's End, The Time of Angels, The Pandorica Opens, Journey to the Centre of the TARDIS, Empress of Mars, The Doctor Falls) In some cases, the Doctor had to disable the isomorphic controls to enable them to do so. (AUDIO: Other Lives) The controls were only isomorphic when the Doctor bothered setting them up that way. (PROSE: Original Sin) The controls of a Battle TARDIS were partly isomorphic. While this did not allow the TARDIS to fully reject the commands of a group of boarding Daleks, it was sufficient to bar them from full control. (AUDIO: All Hands on Deck)

The Tenth Doctor claimed to the Aquabi that his TARDIS key was isomorphic. (AUDIO: Pest Control)

Gwen Cooper lied to Rex Matheson that the Eye-5 contact lenses were isomorphic. (TV: Dead of Night)

Kazran Sardick's machine had isomorphic controls. When Kazran told the Eleventh Doctor this, the Doctor initially said, "Fibber". After Kazran operated the controls when the Doctor was unable to, the Doctor conceded the controls were isomorphic. After the Doctor changed Sardick's personality, they no longer recognised him. The Doctor stated that Kazran's father Elliot, who had set up the isometric controls for him in the original timeline, would not have done so with the altered Kazran. (TV: A Christmas Carol)

The TARDIS possessed the ability to have individuals bio-locked out of the controls to prevent unauthorised operation, as the Twelfth Doctor did for Missy. (TV: The Eaters of Light)