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Cristofori's great success was in solving, without any prior example, the fundamental mechanical problem of piano design: the hammer must strike the string, but not remain in contact with it (as a tangent remains in contact with a clavichord string) because this would damp the sound.
Some Bösendorfer pianos extend the normal gamut downwards to F0, with one other model going as far as a base Piano Lessons C0, making a full eight octave range. These extra keys are sometimes disguised under a minuscule hinged lid that can be flipped down to dress the keys in disposal to avoid visual disorientation in a pianist unfamiliar with the extended keyboard. On others, the colours of the extra white keys are reversed (black instead of white).