In my various Motor cars fitted with normally aspirated petrol engines fitted with Carburettors, I often fitted a Vacuum Gauge directly connected/piped to the inlet manifold, to register manifold vacuum.
The Gauge dial was coloured Green, Yellow, and Red and the needle registered the Vacuum in these areas.
For economical cruising the needle should be kept in the green area, with the foot lifted off the throttle (greatest vacuum). Entering the red area indicated the throttle was being pushed down unnecessarily hard (breaking the vacuum), therefore; "wasting fuel!".... ...!
I wonder if there is a default Sim Vacuum Gauge which does the same job, for normally aspirated, carburettor, Piston engined aircraft?
Paul...G-BPLF...FS 2004...and a 1931 Brooklands Riley 9... 8-)...!