By contrast, nearly all other woodwind instruments overblow at the octave or (like the ocarina and tonette) do not overblow at all. A clarinet must have holes and keys for nineteen notes, a chromatic octave and a half from bottom E to B, in its lowest register to play the chromatic scale. This overblowing behavior explains the clarinet's great range and complex fingering system. The fifth and seventh harmonics are also available, sounding a further sixth and fourth (a flat, diminished fifth) higher respectively; these are the notes of the altissimo register. This is also why the inner "waist" measurement is so critical to these harmonic frequencies.