Hello from Paris!  I am trying to explain coding particulars in the
expression channels of Duo-Art rolls.

Indeed, from time to time, Theme holes (Theme levels) are perforated
without the "snakebite" accent holes being active at the same time.
I think it is a way to close the spill valve without changing the
accompaniment level, and perhaps increase the suction in the expression
box to make the accompaniment regulator more efficient (to play chords
at low level, for example).  Is there another goal?

On the other hand, there is from time to time a snakebite hole without
Theme level perforations; I have not a real meaning for such coding.
Are there people who have ideas about all that?

Kind regards,
Vincent Thébault
Paris