A subspace variance was a phenomenon in subspace that is created by a cloaked ship at warp. In 2371, Jem'Hadar vessels detected a subspace variance from the cloaked USS Defiant. T'Rul advised Benjamin Sisko to have the Defiant drop out of warp to stop the variance. (DS9 episode: "The Search, Part I") In 2383, Sisko ordered the USS Defiant to drop out of warp while cloaked to eliminate a subspace variance. Wheeler Stinson was unaware of the phenomenon. (ST - Typhon Pact novel: Plagues of Night)