The Middle C

[Meffy]

Also, in parts of Europe a "milliard" is a thousand millions, what Americans call a "billion." In America, a "milliard" is the wrong way to spell either 1) the first name of President Fillmore, these days more famous for the Hyundai "soap on a rope" TV advert than anything he did as President, or 2) the yard outside a mill.

[mistertoast]

How do we know we're playing Mozart and Beethoven in the right octave?

I assume it's because of the limitations of certain instruments they used.

So what was the middle C for them? C3?

[Meffy]

Mozart and Beethoven [...] what was the middle C for them?

The Mediterranean.