The chromatic button accordion is a unisonoric instrument with right-hand buttons arranged in chromatic order on diagonals. On a "C-System" chromatic, the outermost row contains the "C" note, and pitch increases by moving in a diagonal down and inward; on a "B-System" instrument, the "B" note is in the outermost row, and pitch increases by moving in a diagonal down and outward. The inner rows of a 4-, 5-, or 6-row instrument duplicate notes on outer rows for greater flexibility in reaching a particular note. A 3-row model lacks this feature. The left hand is a Stradella-type bass arrangement, free-bass, or a converter which can be used as free-bass or stradella.