Randomiser The Randomiser was a device that would ensure a TARDIS would land at unpredictable times and places . Function . The Randomiser , when activated , scrambled the TARDIS ' co - ordinate settings , giving the Doctor even less control than usual over the destination of his ship . As the name implies , using the Randomiser could send the TARDIS to any point in time and space . The Randomiser operated by using a seed code to calculate algorithmic impossibilities , making it possible to predict the destination that would be chosen by the Randomiser if others had access to the seed code ( PROSE : " The Banquo Legacy " ) . When the Time Lords caught up with Compassion after learning the original code , the Eighth Doctor attempted to evade them again by using 8 . 23 as his new seed code based on a bad experience his companion Fitz Kreiner had with wasps as a child - he was stung twenty - three times after finding a nest when he was eight - reasoning that it was a number the Time Lords couldn ' t predict based on their knowledge of him and noting that the seed code simply had to be random rather than complex ( PROSE : " The Ancestor Cell " ) . History . After his successful completion of the quest to find the Key to Time , the Fourth Doctor feared the vengeance of the Black Guardian . Reasoning that if he himself did not know where he was going , neither would the Guardian ( and thus the eternal Black Guardian would be unable to pursue or act against him ) , he installed the randomiser in the central console . ( TV : " The Armageddon Factor " ) The Doctor frequently chose to override the device when it became necessary to visit a specific time or place . ( TV : " City of Death " , " The Creature from the Pit " ) In the end the Doctor chose to take his chances with the Black Guardian , removing the Randomiser as its components were needed within the Tachyon Recreation Generator on Argolis . He made no effort to replace the device despite his earlier concerns , due to his annoyance to not being able to choose where he wanted to have his adventures . ( TV : " The Leisure Hive " ) Later , in his eighth incarnation , the Doctor found himself being pursued by the Time Lord s and was forced to install a second randomiser into the humanoid TARDIS Compassion . While the first randomiser was constructed by the Doctor himself , the second device was purchased on the planet Yquatine . Installing the device caused Compassion great pain , which the Doctor had not anticipated . Possibly due to this traumatic experience , the second randomiser could not be removed or deactivated for some time . ( PROSE : " The Fall of Yquatine " ) Compassion was eventually able to expel the remains of the randomiser , along with her occupants , into the Edifice . ( PROSE : " The Ancestor Cell " ) In his tenth incarnation , the Doctor used the randomiser to travel to the 13th moon of the 13th planet of the 13th galaxy . ( COMIC : " Triskaidekaphobia " ) He later travelled to Ood - Sphere with Donna Noble , claiming to have set the controls to random . ( TV : " Planet of the Ood " ) The randomiser was mentioned in River Song ' s diary ; she thought it was funny to turn it on when the Eleventh Doctor wasn ' t looking . ( GAME : " The Eternity Clock " ) Iris Wildthyme once activated the randomiser on her TARDIS to evade a Monstron time destroyer . ( AUDIO : " Iris Rides Out " )