For a long time a was wondering how this thing ( adjustment for the tuner) is made. Now a found an article about this, but is it Japanese language. Well maybe someone will find it useful. ( I use Google translate)
http://bluess.cocolog-nifty.com/labo/2016/10/yamaha-ct-600-f.html
http://bluess.cocolog-nifty.com/labo/2016/10/yamaha-ct-600-f.html

