In this system, each of two stereo channels is carried independently by a separate groove wall, each wall face moving at 45 degrees to the plane of the record surface (hence the system's name) in correspondence with the signal level of that channel. By convention, the inner wall carries the left-hand channel and the outer wall carries the right-hand channel. While the stylus only moves horizontally when reproducing a monophonic disk recording, on stereo records the stylus moves vertically as well as horizontally. During playback, the movement of a single stylus tracking the groove is sensed independently, e.g., by two coils, each mounted diagonally opposite the relevant groove wall.