The treble side of the Schwyzerörgeli (Swiss Organ) resembles a 3-row diatonic button accordion, but on the left (bass) keyboard, the keys travel parallel to the bellows, and are unisonoric. More specifically, the treble side has two regular diatonic rows, and a third diatonic row that is more irregular in layout but allows for playing in a few extra keys. Thus while the first two rows are usually in B flat (outside row closest to hand) and E flat (middle row), the third row allows the player to get Ab, Db and Gb also, as well as facilitating the fingering in Bb and Eb. The basses typically are two rows consisting of 9 major chords and the 9 corresponding bass notes, progressing in 4ths as on a Stradella bass system common to piano accordions and chromatics, but in the opposite direction.