Triangles formed by buttons in staggered arrangement.

The buttons on keyboards, or button boards, of bellows instruments are most commonly arranged in staggered rows, except on English type concertinas, and the rows may be straight, as on diatonic and chromatic accordions, or curved as on bandonions, Anglo concertinas and Chemnitzers.

The staggered buttons can be seen as forming a grid of interlocking triangles, where each button forms a point of at least two different triangles. Contiguous sides of triangles form parallel rows, from side to side, and diagonal lines in different directions, 1st diagonals and 2nd diagonals.

triangles	rows	1st diagonals	2nd diagonals