Hass notation uses a pitch-proportional chromatic staff whose lines are spaced three semitones (a minor third) apart. Three notehead shapes are used: an oval on lines, and upward and downward triangles in the spaces. This regularly alternating pattern of three noteheads corresponds directly to the three rows of a chromatic button accordion, which has an isomorphic layout.
Stems are horizontally centered on the noteheads, rather than placed at the left or right as in traditional notation. Rhythmic notation is traditional. Pitch nomenclature follows the traditional German pitch names for the naturals (which use H for the pitch a half-step below C and B for the pitch a whole step below C), and the new names O, S, V, and I for the traditional C#, D#, F#, and G#. The pitches of the chromatic scale (from C to C) are therefore:
C – O – D – S – E – F – V – G – I – A – B – H – C
Hass’s original version of the staff has five lines and does not cycle at the octave (MNP criterion 9). To meet the MNP criteria, Hass designed the newer 3-line version shown here, which duplicates the lowest three lines of the “E” clef in his original version. C# (“O”) is on a ledger line. This staff is the same as that of the Numbered Notes system by Jason MacCoy. The pitch nomenclature, noteheads, and stem placement differ.
First Introduced: 2014
Source: Peter Hass, chromatic-staff.dk website