論文アブストラクト：We present a system that, implemented as an iPhone app controllable from an Apple Watch, can help a blind person backtrack a route taken in a building. This system requires no maps of the building or environment modifications. While traversing a path from a starting location to a destination, the system builds and records a path representation in terms of a sequence of turns and of step counts between turns. If the user wants to backtrack the same path, the system can provide assistance by tracking the user's location in the recorded path, and producing directional information in speech form about the next turns and step counts to follow. The system was tested with six blind participants in a controlled indoor experiment.