These go vertically down the side, pointing inward, toward the bellows, making them accessible to only one hand while handling the accordion.

[2] Another source claimed the first piano accordion was introduced in 1854 at the General German Industrial Exhibition in Munich.

It was showcased by the instrument builder Mattäus Bauer and quickly became a serious competitor to button accordions.

The piano keyboard layout was also promoted by the fame of Vaudeville performers Guido Deiro and his brother Pietro who premiered the instrument on stage, recordings and radio.

"[5] (See Accordion music genres) As of 1972 it could be largely said that the piano system dominated the English-speaking North American continent, Scotland, and certain East European countries, while differing button systems are generally to be found in Scandinavia, France, Belgium and former Soviet countries.