The Tissue Compression Eliminator (or TCE), also called a decompression eliminator, (AUDIO: The Evil One) was a trademark weapon of the Master as he fought UNIT, searched for new life in his decayed body, and especially after he assumed the appearance of the Trakenite Tremas. (TV: The Keeper of Traken) He admitted that he wasn't sure about the name, if it eliminated victims through tissue compression or if it, in fact, eliminated tissue compression. (AUDIO: The Two Masters)
Function
As its name suggested, the TCE kills by drastically compressing the bodies of its targets to the point where life functions ceased. Eventually, the victims were no longer visible after the exposure. The Master liked to leave the shrunken doll-like corpses of his victims as a calling-card for the Doctor to discover. (TV: The Deadly Assassin)
The TCE, despite its name, was equally capable of shrinking inorganic tissue: victims' clothes were also shrunk. On one occasion, the Master demonstrated the weapon by shrinking empty space-suits. (TV: Planet of Fire)
According the Sally Armstrong, it usually compressed people by a factor of 10. (AUDIO: Eyes of the Master) The Reborn Master gave Sally a TCE which also acted as a communicator. (AUDIO: The Reviled)
History
The Master used the TCE to kill Goodge to infiltrate a radio telescope for the Nestene Consciousness. (TV: Terror of the Autons)
He once materialised his TARDIS within UNIT HQ and attacked the Third Doctor. In the brawl, the Doctor took the TCE and the Master fled.
The Doctor threatened the Eighth Doctor with the TCE, hoping he would hand over the TARDIS. Ultimately, he decided against it and handed the device to his future self. (PROSE: The Eight Doctors)
Before his disfigurement, the Thirteenth Master decided to "spice things up a bit" by using a staser instead of the TCE. After swapping bodies with a future self, AUDIO: The Two Masters) he returned to using the TCE. (TV: The Deadly Assassin)
The Fourth Doctor once described the method by which the Master killed as "matter condensation". The Master at the time used it to kill a camera technician. (TV: The Deadly Assassin)
The Fifth Doctor was able to use the TCE to sabotage the Tremas Master's TARDIS. (TV: The King's Demons)
The Tremas Master later attempted to improve the design of his weapon, but a laboratory accident resulted in the laboratory and him both being reduced in size instead. This did not appear to harm him. (TV: Planet of Fire)
On another occasion the Master used the TCE against a velociraptor revived by the fountain of youth. However, it landed right back in the fountain, re-emerging unharmed but miniscule in size, making a comical sight. (PROSE: A Town Called Eternity)
The Sixth Doctor stole and used it to threaten the Tremas Master and the Rani; later Peri Brown did the same. (TV: The Mark of the Rani)
During his first encounter with the artificially-enlarged mechanoid freelance peacekeeping agent Death's Head, the Doctor used a TCE (which he happened to have on him) to defend himself against the mercenary. Death's Head was not injured, but found himself returned to his original size (that of a normal humanoid), which he remained for the rest of his career. (COMIC: The Crossroads of Time)
Izzy Sinclair was shrunk after being shot with a TCE without being killed outright by the Master's disciple Sato Katsura. She was later able to use the weapon to reverse the process. (COMIC: The Glorious Dead) He also gave one to Sally Armstrong (AUDIO: Eyes of the Master, The Reviled)
The TCE was used by Es'Cartrss of the Tactire through a simulated reality in the Matrix of the Doctor's TARDIS, while posing as the Valeyard. (COMIC: The Forgotten)
Replacement
Following his regeneration into "Harold Saxon", the Master used a laser screwdriver in lieu of the TCE. (TV: The Sound of Drums)