On Stradella-bass instruments, the left is logically arranged with chords arranged in fifths vertically (like C-G-D-A-E...) and chord types horizontally (Root note, alternate bass note, major, minor, seventh, diminished). In addition to the Stradella instruments, a "free-bass" piano accordion also exists with buttons that produce single notes.
Instruments vary in the number of bass buttons from 12 to 120, with the higher numbers allowing greater flexibility and chord choices. All piano accordions produce the same note on press and draw of the bellows.
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