The Anglo (Anglo-German) System Explained:

• Was developed by Carl Friedrich Uhlig in 1834 (5 years after Wheatstone invented the English) in Chemnitz, Germany.
• Are related to the melodeon and the harmonica in the way their scales work.
• Has low notes on the left hand side and higher notes on the right. The rows nearest the player’s wrist form a single scale in one of the set  musical keys of the instrument. The other rows are the scale of the other musical key referred to in the instrument description.
• Has 20, or more usually, 30  buttons (adding a third row to each side with all the additional sharps and flats to make the instrument chromatic, but not necessarily easy to play in all keys).
• Is described or designated  by its playing musical keys typically C/G; Bb/F etc and by the number of buttons it has, so typically a 30 button D/G concertina.
• Plays different notes on any button depending on which way the bellows are worked.  The need to change bellows direction frequently lends its self to rhythmic styles of play.
• Is used for song, solo, some ensemble, session play and prized for rhythmic dance.
• Generally switch instruments to play in different keys.
• Is probably the most expensive of the concertina family.