birdcage primer?

[Kazuo Yoshizaki]

I first open the bottom board and put a temperament felt strip just
above the bridge, underneath the keybed. Set the temperament, tune the
middle strings as far as the temperament strip goes. Tune unisons by
removing the strip one by one. Tune octave using a Pap's mute in the
treble, and a regular rubber wedge in the bass (insert underneath the
keybed).