So you truly need seven
tone holes and an overblowing hole. Learning how to play higher registers on woodwinds like a recorder is therefore rather simple, and it makes things easy for the tool maker: The tone holes and their distances for the upper octave are accurately an analogous as for the lower octave. Now overblowing works on clarinets, too, but the effect is various: The clarinet overblows not to the eighth tone on thescale an octave which is exactly double the frequency but to the 12th tone. The Italian word for here's duodecime,and so we call the overblowing key the duodecime key. A beginner must learn this and get used to it. Furthermore this has implications on the building of the instrument: First it needs more tone holes than octavating contraptions, as a result of if you want
to play scales up, note 9, 10 and 11 need their own tone hole.