The machine consists of two seperate machines: a recorder, and the master machine. The recorder, which Carter describes as a strange looking machine, the face of which is covered with innumerable dials and with a number of heavily insulated cables attached to it, is capable of recording a person's nerve index, which is unique for every individual. To do so a person is strapped to the machine in something that looks like a straight jacket, and put through a series of examinations that tests the person's responses to torture, kindness, and fear. The person also has to answer a series of questions. The recording feels like countless needles touching every part of the person's spine.
The Master Machine records all the individual nerve indexes, and is capable of generating short wave vibrations which can be keyed exactly to a individual person's nerve index. When doing so, it causes a severe paralytic stroke that kills the person almost instantly. It is described as being very delicate, one can easily destroy it.
The machine was originally designed to keep prisoners and slaves from fleeing Kamtol, fearing they would spread the word about the lush, fertile valley to other countries which would most likely try to conquer it. Jeddak Doxus however quickly realized the machines possibilities and started recording the nerve indexes of all inhabitants of Kamtol, except his own. This way he could keep the entire population under control and reign supreme. The original inventor was disgusted by the fact that Doxus abused his invention for this purpose, and as a result Doxus had him killed. He took the secret of the machine with him into his grave however. After his death the inventor Myr-lo was appointed by Doxus to maintain the machine, but he did not have the genius needed to build a complete new one, only to maintain the old one.
The dreaded machine was eventually destroyed by John Carter when he was captured by the First Born, freeing the population of Kamtol from Doxus.