The extension of a standard blues harp is three octaves, but they are not complete. Even the major scale of the same key of the harmonica is found only on the middle octave, holes 4 to 10. To play exactly the same scale on the low octave, holes 1 to 4, you have to play a couple of bendings. On the best octave, holes 7 to 10, another bending must obtain the whole level.