Since I began to also use my diatonic 'harp, it seems reasonable to show its layout.
The 'harp is a Korean made Oscar Schmidt OS-110-21 with fine tuners that I acquired in the summer of 1998. I took it with me to MLAG 1999 where it got fitted with Chuck Daniel's action lowering device. I played it as a chromatic 'harp until early 2002.
In February 2002 Mike Fenton converted it into an F/C diatonic, simply by lowering all strings for sharp notes one semitone, except for the a# strings (shown below as bb). So the string schedule is left to right / bass to treble as follows:
f g c d e f f g a bb b c d d e f f g g a bb b c c d d e f f g g a bb b c
In order to have the chord button layout closer to my chromatic layout, I changed Mike's original one slightly. Now it looks like this:
------------------- side of the treble strings -------------------
Csus4 C6 Bb F C G Dm7
Fsus4 F6 C7 G7 D7 Gsus4 X
Gm7 Gm Dm Am Em LF LC
------------------- side of the bass strings -------------------
X means empty bar, LF and LC are the lock bars for F and C. The locking is achieved by sliding the respective button under the chord bars cover; this is facilitated by part of the plastic button material being removed: the lock buttons have now a step shape.
Note that because of the special nature of the autoharp the following equations hold:
Gm7 = Bb6, Dm7 = F6 and Am7 = C6
Over the years the chord bars' clacking got annoyingly loud (perhaps one reason for leaving the 'harp alone for many years). But during Sore Fingers Week 2012 Greg Schreiber took care of it and the clacking has vanished.