I believe the disadvantage of depending entirely on the tuning aid
("tuning without listening") is that the electronic tuning aid
assumes that the piano being tuned has the same behavior as the
average piano data stored in the electronic tuning device.

Well, the modern mass-produced Yamaha pianos are as alike as peas
in a pod, so this works okay.  But, in the remainder of the world's
pianos, the acoustic behavior can vary considerably from the average,
and so tuning using only the electronic aid produces less than
optimum results for that particular piano.  The experienced piano
tuner, using his ears, listens to the piano for the final stages of
the tuning; the tuning aid can only do tuning without listening.

So what's optimum?  What's a good job?  Most customers will be
satisfied with any improvement, but some will demand more, so those
questions are best answered by the customer.  That's why the
electronic tuning aid doesn't have a little indicator that says,
"Stop -- The piano is now perfectly tuned!"  ;-)

Robbie Rhodes
Etiwanda, Calif.