The [Conn] strobe and the Korg devices are good references for a
decent, if not good, tuning on a big old upright and a quality grand
(from my experience).  Tuning charts can be a poor reference on small
and badly scaled pianos.  Equal temperament tuning is the standard used
by the vast majority of piano tuners.

I know a tuner who uses a Korg.  He does the temperament with the
machine and makes the octaves beatless by ear.  Equal temperament it
ain't, but he can satisfy 90 percent of his customers (according to
him), and I tend to believe it.  The Sight-O-Tuner can be bought for
under $100.  Using the Sight-O-Tuners concert tuning method, a very
good custom equal temperament tuning can be had in most cases.

I don't recommend any of these devices for professional use.  If I just
tuned my own piano I would probably use one of them.

Bill Maguire