There are at least two electronic tuners that I am aware of.  About six
years ago, I bought one for $55 at my local music store that rents and
sells musical instruments.  It is the model ST-1000 made by the Sabine
Musical Manufacturing Co., Inc., 4637 N.W. 6th Street, Gainsville, FL
32609.

It works on an even-tempered scale, 12 notes per octave, and has a seven
octave range (C1 through B8).  It is normally calibrated to A440, but
can be readjusted to match another instrument with the push of a
button.  The unit is easy to use with its L.E.D. display.  There is one
light for each of the twelve half steps plus "in tune", "flat" and
"sharp" lights.

The only difficulty I have experienced with the unit is that a piano
cannot be tuned in its lowest and highest notes which are outside the
range.  These have to be tuned by ear.

Musicmaker's Kits, Inc. also sells a unit with an analog needle display
for $100.  It is also seven octaves.

Incidentally, they also sell a hurdy gurdy kit if you want to see a
picture of one style of this mechanical instrument, or better yet want
to build one.  I have built one of their Hammered Dulcimer kits, and
they are of excellent quality.  They can be reached at:

Musicmaker's Kits, Inc., P.O. Box 2117, Stillwater, MN 55082-3117
tel 612-439-9120 or 800-432-5487.  Also www.musikit.com and email
at info@musikit.com.

Hope this helps.

John Breen