Hi All,  All Duo-Art accordion pneumatic boards measure 3" x 3".
The thickness of the three moving boards in the center is 3/8".
The thickness of stationary bottom board is 1/2" and the thickness
of the moving top board is 1/4".

When calibrating the distance between the boards, they should be set
as Jack Scarsbrook explained earlier.  However, when the leather is
replaced, it is wise to use the special Duo-Art Expression Accordion
Spacer Blocks sold by Player Piano Co.  Using them will ensure that you
have enough extra space between each section to allow for the thickness
of the leather.

Put another way, if the spacing between the top board (or the #5 board)
and the #4 board is only 1/16", then it is physically impossible for
that step to move the required 1/16" because the leather is pulled into
the space between the boards (by the vacuum) and the leather folds over
on itself.  This is also true, to a lesser degree, with the other three
steps.

If the above were not the case, the total distance required between the
top and bottom boards would only be 2-13/16".  However, in practice the
total distance is 3-1/4"

Musically,
John A Tuttle
Player-Care.com
Brick, New Jersey, USA