"All four individual players must be able to _feel_ the tempo they are
playing in the same way. I believe it was Mahler who once gave out a
beat very distinctly--one, two, three--told his orchestra players to
count the beat silently for twenty measures and then stop. As each
_felt_ the beat differently from the other, every one of them stopped at
a different time. So _tempo_, just like intonation, must be 'tempered'
by the four quartet players in order to secure perfect rhythmic
inflection.