It is basically a quality control tool for carburetor rebuilders. They test carburetors at different depressions to a known good "reference" carburetor. I find it handy when adding or modifying the power valve circuit or with adjusting the main jet when changing to a booster with more signal.
Hi Unitedauto, that is a cool bench. Thanks again for sending me copies of the manual.
My bench is coming along, working on it in my spare time.
I'll post some pictures of my progress.
Engineer2, the motor that drives the vacuum pump is a 3 phase 10 hp motor
(I am also in the Chicago burbs)