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depends on model
The Anglo concertina has the bass notes at the left side and makes other tones pushing than pulling a button.
The English concertina makes the same tone pushing and pulling a button.
The duet concertinas have the bass notes at the left side and make the same tone pushing and pulling a button. The Hayden duet concertina has the same fingering for all scales. It has a shifted 6-plus-6 keyboard layout.