It is difficult to imagine that valve travel is so critical that
a few thousandths of an inch would matter.  However, there may be a
better parameter to measure if consistency of valve action is the goal.
I use a different method with some theoretical justification but would
like to hear the opinions of others.  First the justification.

The goal is to achieve equal rate of flow.  Setting the valve travel
will accomplish this as long as the valves are perfect in a few respects.
The top and bottom faces must be parallel and they must be perpendicular
to the valve travel.  A crooked valve will straighten out but the total
travel will be different from that of a straight valve that has equal
flow.  So by setting the travel you may not be setting the flow the
same if the valve is crooked.

I use a flow meter that measures the flow through the top valve plate
and top valve leather.  Ideally both the top and the bottom flow
should be measured but it is difficult to shuttle the valve to the top
seat and also measure the flow at the bottom seat at the same time.
It could probably be done but measuring the top flow is easier.  If you
are concerned with leather compression influencing the readings, you
can apply vacuum to the stack while measuring the flow at the top seat.

I have a rotameter flow meter that covers the range of the Ampico and
Duo-Art stacks that I have rebuilt.  I also have an electronic flow
meter that can be set to cover almost any range.  It is an electronic
pressure sensor connected to a cheap data acquisition module.  The
sensor measures the pressure (or vacuum) drop across a restricting
orifice.  USB data acquisition units can be found for less than $50.

The pressure sensor that I use is an evaluation board for a SenSym
(I think their name has changed) sensor that was also very cheap but is
no longer made.  There is probably something else cheap and available
that would do the same.  The one I have has a bridge amplifier and
various adjustments to make it useful for all sorts of fun things.

I compared dial indicator readings to flow measurement on a Duo-Art
stack and they followed each other very closely.

Best regards,
Spencer Chase