Abstract: The musical slide rule has a base listing two sets of musical note symbols, each set arranged in two columns. The base is imprinted on both sides. The cover has apertures in each side and is slidable on the base. One side is the flat (♭) side, and the opposite side is the sharp (♯) side. There are also ways that the user will know that the wrong side is being used. Aligning the apertures of the cover with a musical note symbol on the base gives the user information such as the notes of the major and minor scale for that note, and chords for that note.