In the
lying position, on the side part of the upper body (1), the uppermost part of the surface of the second button (2), constituting the end of the second lever of the "c" flap is located at the height X
ranging from 1.5 to 3 mm, and preferably 2 mm, measured from the uppermost part of the surface of the first button (3), which runs parallel to the horizontal planeconstituting the end of the first lever of the high "e" flap. The uppermost part of the surface of the third button (4), constituting the end of the third lever of the "b" flap is located at the height Y
ranging from 12 to 14 mm, and preferably 13 mm, measured from the uppermost part of the surface of the first button (3), which runs parallel to the horizontal plane, constituting the end of the first lever of the high "e" flap. In the
lying position, on the side part of the upper body (1), the uppermost part of the surface of the forth button (5), constituting the end of the forth lever of the high"f sharp" flap is located at the height Z
ranging from 14 to 16 mm, and preferably 15 mm, measured from the uppermost part of the surface of the first button (3), which runs parallel to the horizontal plane, constituting the end of the first lever of the high "e" flap. The uppermost part of the surface of the fifth button (6), constituting the end of the fifth lever of the "f sharp" chromatic flap is located at the height V ranging from 16 to 18 mm, and preferably 17 mm, measured from the uppermost part of the surface of the first button (3), which runs parallel to the horizontal plane, constituting the end of the first lever of the high "e" flap.