C♯ Phrygian dominant

C♯1D♭2E♯3F♯4G♯5A♭6B♭7

The fifth mode of harmonic minor: a flat second over a major third, so the step from the second to the third is a step and a half.

The same sounds spelled from the other side are D♭ Phrygian dominant.

Written out

Fig. 2 · C# Phrygian dominant, ascending

Every accidental is written in, rather than left to a key signature, so the letters can be read one at a time.

C♯HDW+HE♯HF♯WG♯HAWBWC♯

C♯ Phrygian dominant is C♯, D, E♯, F♯, G♯, A and B, and back to C♯.

Its steps are H – W+H – H – W – H – W – W, where W is a whole step and H a half.

On the same tonic, C♯ Phrygian differs from it by exactly one note.

Across the first twelve frets of the guitar its notes fall in 45 places, which is what makes a scale a shape rather than a list.

Found by testing every chord in the catalogue against these 7 sounds, not chosen.