A device includes a rectangular base A engaging with two cursors B and C, the base and the cursors having musical data thereon that relate to notes, scales, tonalities, intervals and chords, and that analytically provides said data with regard to the fundamental rules of harmony. The rectangular base A includes a central longitudinal slot in which the first cursor B slides and the second cursor C slides over the base A and the first cursor B. The device is suitable for use by musicians in general and, more particularly, for instructional use.