Arthur,  I built a flow meter along the lines of the one Phil Dayson
demonstrated at the Seattle MBSI convention.  The one I built had
mechanical gauges rather than the liquid ones that Phil used, but it
operates on a similar principal.

I have used it extensively and it works just fine.  In fact, I have
given two workshops at MBSI meetings, based on its use.  It's especially
good at tracking down tiny leaks.  I can measure air leaking through a
piece of wood; air through a piece of bellows cloth or leather is a
snap.

It would be a simple job to set one of your bleeds to a reasonable flow
rate and then just set the remaining ones to match.  You could also
keep track of whether the one you set had changed during the process.
You'll need a small vacuum cleaner and a Variac [adjustable transformer]
as a vacuum or pressure source.  I used what I call a "Phil-ter Queen"
in Phil's honor.

Regards,
Craig Smith

By the way, if you use a liquid manometer, make sure you put a liquid
trap in the line to avoid sucking your manometer fluid into your
"Phil-ter Queen".