Notes: C, D, Eb, F, G, Ab, A, and Bb - Key: C - Origin: Church - Category: Nonatonic or Ennatonic Scales
The C Gregorian no.1 uses nine notes per octave. Because of this same reason it is a member of the so called Nonatonic or Ennatonic -scales that have Nine-note (or Nine-tone). On the piano keyboard, it is made up of three black keys: Eb, Ab, and Bb and five white keys: C, D, F, G, and A. This combination makes this scale - as well as the C Gregorian no.2, C Gregorian no.3, and C Gregorian no.4 - as great choices for composing or improvising Church music.
If we take a look a the key signature of the C Gregorian no.1 Scale we can find it has three flats and no sharps. Therefore, on sheet music you will find three accidentals on the score. The notes of this scale are: C, D, Eb, F, G, Ab, A, and Bb.