Unisonoric Bellows Driven Instruments

Unisonoric instruments, produce one and the same musical note at each button in both directions of the bellows and are often referred to as chromatic instruments they have all the notes of the chromatic scale, that is twelve notes each separated by a semitone interval, known as the 12 note equal tempered system.

Broadly speaking, unisonoric instruments can be divided into three groups. Isomorphic or neutral on the one hand, or non-isomrphic or home-key biased on the other, as well as a third hybrid group.

Isomorphic Layouts

Neutral or isomorphic layouts arrange musical notes so that there is always the same musical interval between between keys or buttons that have the same spacial relation between them at any place on the keyboard. This enables the same, "iso", shape, "morph", to be used to play the same kind of scale, chord, arpeggio etc. in different musical keys.

International chromatic layout
Wicki Layout

Non-Isomorphic, C Major biased layouts

Non-isomorphic layouts are usually based around a core of notes from the diatonic scale of C Major, with accidentals notes found at buttons surrounding or on either side of this core.
Piano Keyboard
Maccan Duet Concertinas

Unisonoric Hybrids

These instruments usually have a core isomorphic layout surrounded by or placed next to several other notes that extend the range or make it easier to play very broad chords. These notes are not arranged isomorphically.
Unisonoric bandonions