The chromatic accordion evolved in the 1850's by F. Walter, the original model was a one row diatonic invented in China, this was. the original concept of the accordion. However, the Diatonic Accordion capable of a chromatic scale of 46 notes,  was the prototype on which the chromatic accordion was created.  A rearrangement of the reeds and a Chromatic Button Accordion was born. Chromatic Accordions come in several systems, 3 rows, 4 rows, 5 rows and 6 rows, rows 4, 5 and 6 are repeats of the first 3 rows.  The two most popular systems are the B and C system, B system has become more popular in these latter years in the UK in competition, C system is the commercial choice.  The bass systems can be stradella, free bass, or converter bass.  The possibility to perform classical transcriptions as they were written, or contemporary music written specially for this system. The Bayan Accordion, is used in Russia mainly, but is gaining popularity worldwide.