Each adjustment changes the engine RPM. Each RPM change also changes the vacuum reading, including on the master carb. What is the vacuum reading on the carb not attached to a vacuum gauge?
Anyway, the only hope would be to keep one gauge on the master carb, and sync each of the others to it, in turn.
But sometimes, having a cross point screwdriver AND a straight slot screwdriver is better then using the straight slot screwdriver in the cross point screw. It's a best tool for the job thing.
Cheers,