Reversal loop

A reversal loop was a technological functionality.

Box's circuits contained a "synchronised reversal loop", a telltale marker of Sun Builder technology as it was a miniature form of temporal circuitry, meaning that Box's processing units "actually sent back their reply slightly before they’d been asked the question". The loop emitted a chronon shimmer. (PROSE: Out of the Box)

The DoctorDonna used an internalised synchronous back-feed reversal loop in order to prevent Davros's reality bomb from detonating. The DoctorDonna enabled this mechanism from the Crucible's control console. An internalised synchronous back-feed reversal loop was capable of closing all Z-Neutrino relay loops. (TV: Journey's End)