Hi folks!  I read with interest some earlier postings on how the
Duo-Art mechanism works.  As I understand it, the snakebites at each
end of the tracker bar shift the corresponding half of the keyboard
to the theme momentarily.

Can somebody please explain what happens in the case of my Steck
upright with only one expression box.  The four holes at the lower end
of the tracker bar are connected to the one expression box, presumably
to control the accompaniment.  However, the upper and lower snakebite
holes are also connected to valves.  If there is no theme expression
box, what do the snakebites control?  Is it the Themodist mechanism?

Ian Sanderson