It is refreshing to receive a contribution from Bob Billings [110702
MMDigest], and his study of Recordo roll expression coding is the
primary reference for all of us who have Recordo rolls.

My interpretation of the photograph of Craig's expression box is that
it is a 5-level choker type of expression box.  It is 5-level because
the individual pneumatics operate on the same shaft and the fixed part
of each pneumatic is fixed to the box and not to the moving part of
the next higher expression pneumatic.  So the movement of the operating
shaft due to the activation of each pneumatic is referenced to the
expression box frame and not to the next pneumatic, as in the Duo-Art.

There were leaker types and choker types: the choker type maintained
the vacuum level at the tracker system at a high level, whereas the
leaker type gave a low level vacuum across the whole system, which
could cause problems with the tracker operation.

It is interesting that the rewind punchings on Recordo rolls punch
level '8' and level '4' to give level '12' as advised by Bob.  In an
unpublished paper on vacuum levels versus coding system, the vacuum
level at each step is given for 5-step (Recordo 'B'), 7-step (Ampico
A), 8-step (Ampico B), 12-step (Recordo 'A'), and 16-step (Recordo 'C'
and Duo-Art) systems.

Paul Rumpf
Melbourne, Australia