Concertina

A concertina is a musical instrument that makes sounds using air pushed and pulled through reeds using a bellows. The fingers push buttons at both ends of the instrument.
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.