I said manifold pressure, that is the opposite of vacuum, not the same thing. As manifold vacuum goes up manifold pressure goes down. A manifold vacuum of say 30" of vacuum ( a perfect vacuum as that is as high as it will go) is a lower pressure than 10" of vacuum. The atmospheric pressure is pushing the metering rod in because the pressure in the manifold is low. A spring is balancing these forces so that there is equal force on bothe sides of the meter diaphram. As the manifold pressure goes up the increased pressure and spring to gether push's the metering rod up causing the fuel mixture to be enriched.

I usually convert all my pressures to absolute pressure before starting calculations, that way there is less confusion.