At 02:10 PM 7/8/2012, neil n wrote:
>With my DVOM, I'd see the value change at a more or less "even" rate
>when slowly and evenly moving the vane.

The ideal tool for this is a scope.  Analog meter with a twitchy
needle is next.  I'd rate most DMMs essentially useless for it unless
they have a fast-responding bar-graph display.  The normal 2-3
updates per second really can't show you little dropouts unless
you're moving the vane with a micrometer screw or something like
that, and even then I have some doubts.  For one thing, it's not
actually measuring during that whole time between updates.  It spends
part of the time charging a capacitor with the input signal, then
part discharging it at a known rate while counting to determine how
much it got charged.  Then it sits around and waits until it's time
to display the new number and start over.  I'm going to make a wild
guess that a typical DMM is only actually looking at the input less
than a quarter of the time.

Yours,
David