Mr Red, the naming of button boxes gets confusing... As far as I understand it, the ones we normally call melodons lack the full chromatic scale in the combination of thier diatonic rows (forgetting any addional buttons for accidentals) a G/D box is an example of this.

Some boxes which still have diatonic rows have a full chromatic scale between the rows, e.g. a B/C box and I believe they are more likely to be referred to as chromatic accordians.

Jimmy Shand's famous box was a 3 row British Chromatic Accordian - a Hohner Morino which I believe he designed. I believe that "British Chromatic" means that the 2 or 3 diatonic rows are a semi-tone apart from each other. As far as I know the bass of his used the standard piano accordian system.

Anyway, that is how I understand things at the moment. Maybe Bob Bolton or someone else will come along and set me straight.

Jon