Bernard 333, this is the main problem with "el cheapos" parts available now !
I take my camera today and record my vacuum gauge connected in line from the "out" port of the GCV to the Vacuum regulator and you can see the readings on the following video. I don't speak very clearly in the video but you should understand. However, values are printed in the comments window.
http://www.youtube.com/watch?v=OB2-Bpe6lPM
To compare to the figures you gave me Mike, results are setting higher, espacially @idle, I read 10-12hg. What do you think about how the needle reacts from idle to 2800rpm ?