Hi All,  I am in total agreement with John Tuttle's and Don Teach's
comments on electronic tuning aids for pianos.  They are a dead waste
of a shilling (a nickel over there); they do not take into account the
need to "stretch" the tuning as you ascend the octaves or account for
the compression of the frame and soundboard.  The human ear is the only
way to do it and, as already quite rightly been said, it's an art form,
not a science.

I used a sophisticated electronic aid when I was organ tuning.  It was
more efficient for high pressure instruments where the temperature of
the incoming wind would quickly de-tune the notes if you lingered too
long, so that you would be "chasing" the pitch which would necessitate
waiting for the pipe to stabilise.

I tried tuning a piano once this way and quickly gave up and called in
the professionals.  I hated tuning pianos anyway, and tuning barrel
pianos which of course should all be burnt.

Cheers to you all,
Paul Camps (in Great Britain)