Just Keys is a medium upright or console piano that
I tuned in just intonation. In 1990, I restrung this
instrument three times and retuned it four
times. The graphic above shows the complete
keyboard, with Lexan-covered colored labels, from
the first key in the bass to the last key in the
treble.

Note that the B-3
key identifies ratio 1/1, which is the fundamental
frequency of the tuning. This key sounds G1 at 49.0
cps! Since the G-11 key normally produces this
frequency, observe that I eliminated most of the
tones that comprise the first octave of the standard
piano. Consequently, the A-1 key now sounds
frequency ratio 8/5, or a just major third, interval
ratio 5/4, below 1/1, which is Eb1 at 39.2 cps; and
the A#-2 key now sounds frequency ratio 16/9, or a
just major second, interval ratio 9/8, below 1/1,
which is F1 at 43.6 cps.

A 10-tone octave, ratios 1/1–2/1, exists from the
B-3 key to the A-13 key (two keys with two dark
blue labels); a 17-tone octave, ratios 2/1–4/1,
from the A-13 key to the D-30 key (two keys with
two dark blue labels); and another 17-tone
octave, ratios 4/1–8/1, from the D-30 key to the
G-47 key (two keys with two dark blue labels).
From here, three consecutive 12-tone octaves, ratios
8/1–16/1, ratios 16/1–32/1, and ratios 32/1–64/1
span the distance from the G-47 key to the G-83 key.
These 12-tone scales resemble the tuning of a
conventional piano. Short string lengths determined
by the shape of the cast iron plate and the location
of the treble bridge severely restrict alternate
tuning possibilities in the upper treble range.