DG-600 AOA static ports

My DG-600 has paired sets of static ports on the fuselage, just above
the wing roots. These feed the factory installed angle of attack meter.
My meter does not function, and I'd like to construct a replacement.
I assume the AOA meter was simply measuring the pressure differential
between these ports. Would anyone care to guess as to the magnitude of
these pressure differentials?

I believe these meters were installed to address two issues, touchy
stall characteristics at rearward CGs, and helping the pilot avoid
draggy portions of the polar. Does anyone know if the meters were
effective?

Thanks,
Marc