Device which enables the tracker bar, especially of a piano, to shift laterally for up to several notes so as to transpose the music arrangement to a higher or lower range for use in accompanying a singer. The sustaining pedal hole in many tracker bars is several perforations wide, or is located in a separate stationary part of the bar, permitting automatic sustain to work when the music is played in several different keys. Not used in instruments with other control perforations in the tracker bar, because transposing the tracker bar would confuse the controls (exception: some very late Duo-Art reproducing pianos in which only the note-playing portion of the tracker bar shifts).
MBSI
Musical Box Society International