The emergency manual monitor was a compartment located in the engineering section of Constitution-class starships. Overlooking the main engineering deck, entry to this area was gained by use of a gangway.
Distribution of power generated by the warp drive could be controlled from this center. In 2267, Engineer Scott and Doctor McCoy surreptitiously diverted warp power to the transporter in order to escape the mirror universe. The emergency manual monitor aboard the ISS Enterprise was heavily guarded and unauthorized power transfers were monitored by the security chief's panel. (TOS: "Mirror, Mirror")
In 2268, the android Norman made several adjustments to the instruments in the emergency manual monitor, tying the matter/antimatter pods to a trigger relay that would destroy the USS Enterprise if the course he laid in was altered. (TOS: "I, Mudd")
Transporter control was also regulated by the monitor. When the Enterprise was ordered to ferry newly-designed equipment to Memory Alpha, the direct transfer was to be conducted from that location. Later, when the Zetarians interfered with the transporter beam, the problem was to be diagnosed at the emergency manual monitor. It would be brought down to Memory Alpha after the Zetarians are destroyed. (TOS: "The Lights of Zetar")