Square-built button accordion or Concertina developed in the 1840s by Heinrich Band of Krefeld, but similar to the ‘Chemnitz’ concertina of C.F. Uhlig, invented in the previous decade. All early models were diatonic: they produced different notes on the push and pull of the bellows (see illustration). In 1921 a chromatic model was introduced that produced the same note on the push and the pull: this instrument has almost totally eclipsed the diatonic variety. Most bandoneons have two reed banks and no shifts (register changes). Different models may have 64, 88, 104, 106, 128, 154, 176, and even 220 notes; the South American instrument usually has 38 keys or buttons for the high and medium registers and 33 for the lower register. The bandoneon has been used since about 1900 as a solo virtuoso instrument in tango orchestras of Argentina, Uruguay and Brazil. Perhaps its most famous exponent was the Argentine Astor Piazzolla (1921–92). See also Accordion.