The discussion in progress on this topic is good.  Here are some of
my opinions to toss into the fray.

Duo-Art regulation is made difficult by the nature of the expression
box.  The system is clumsy.  Yet, it can be made to work in a delicate
manner.  As has been previously stated, no two pianos are the same.
Ideally, a well regulated Duo Art will mask the clumsiness of the
system and compensate for the myriad variables found within.

Initially, the regulator springs should be just tight enough not to
rattle when the pump is shut off.  Then with the pump on, turn the
regulating screw to achieve a stack vacuum of 5 inches.  This should be
a good starting point.  Measured movement of the regulator pneumatic
with the pump off and on is really meaningless.  Large movement of the
regulator usually indicates a leaking knife valve.

The test roll is used to make the piano conform to the coding used by
the roll editors.  The "play-don't play" tests are the first steps in
calibrating the air flow (cubic volume) through the entire system.
These tests are not intended to set the "sound volume".

The definitions of "play-don't play" are vague.  For example, how many
notes should fail to play in the "don't play" section?  This suggests
that accordion adjustments in this test are not a "point" but rather
a "range".  Once the "play-don't play" tests are complete, the piano is
only roughly calibrated to compensate for "cubic volume" consumption
within the entire system.

It is difficult to thoroughly analyze what is wrong with Ray
Fairfield's piano.  The numbers and the conditions he describes don't
make sense.  If the stack can not go to fifty inches vacuum with the
air motor stopped, the accordions fully collapsed, and correct
regulator springs installed, then regulating the box is for naught.
Something else is terribly wrong -- bad pump, leaking stack valves,
an error within the expression box or even a slipping drive belt.

At this point, the only other thing I can add is don't put a
combination of springs on the regulators.  Use correct springs.  If
that doesn't work, there is a problem with the rebuilding that must
be solved before regulating the piano.

Bob Taylor