Chevrolet Camaro 2018 Owner's Manual Supplement page 8

Instruments and Controls 7
English
This gauge indicates vacuum during
light to moderate throttle and boost
under heavier throttle.
It displays the air pressure level in
the intake manifold before it enters
the engine's combustion chamber.
The gauge is automatically centered
at zero every time the engine is
started. Actual vacuum or boost is
displayed from this zero point.
Changes in ambient pressure, such
as driving in mountains and
changing weather, will slightly
change the zero reading.