Abstract: A cycle derailleur incorporates an indexing mechanism (indexer) as an integral part of the derailleur. More specifically, the indexer is a physical part of the derailleur structure, and is activated by the pull or release of a cable (e.g., operated via gearshift control on a cycle handlebar). Actuation of the indexer requires exertion of a threshold force sufficient to overcome built-in resistance of a detent-style, spring-loaded mechanism. As shifts are made from one gear to another, the indexer is adapted to urge the derailleur into precision alignment with each selected gear. In each of the described embodiments, the indexed derailleur and a method for indexing (digitizing) gear changes by means of, for example, a movable bearing/detent mechanism, are characterized by a deformable parallelogram linkage actuated via the cable through a gearshift control. The result is an improved cycle shifter system that fosters accuracy and avoids derailleur mislocation between shifts.