Abstract: There is disclosed a device of the calculating rule type that is useful in music analysis to assist in spelling chords and determining scales, transposing of chords or notes, identifying key signatures, determining minor keys relative to their major keys, performing chord analysis, determining relationships among chords, and writing of music. The device comprises a base plate member with at least one movable member mounted thereon. There is provided a plurality of 12 indicia representative of the 12 notes of an octave of the musical scale disposed on one of the members in a linear, circle of fifths progression. The other of the members bears an index mark and a plurality of 11 calibration marks in linear progression thereon. Also disposed on the other of the members is a plurality of indicia cooperative with the first plurality of indicia to perform the functions of spelling of chords and scales and of transposing of chords or notes.