Unlike Stradella, every button plays a single individual note across several octaves. This allows the left hand to play complex melodies or custom-voiced chords, similar to a piano's left hand.

The most common system. Buttons are arranged in rows and columns based on the Circle of Fifths .

Most accordions have a dedicated bass section for the left hand. There are two primary mechanical systems used to play these notes:

5 Different Accordion Bass Systems | All About The Accordion Bass Buttons