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If equipped, this gauge is located near the driver side of the instrument panel cluster.
This gauge indicates vacuum during light to moderate throttle and boost under heavier throttle.
This gauge displays the air pressure level in the intake manifold before it enters the engine's combustion chamber.
This 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.
Chevrolet Cobalt Owners Manual. Control of a Vehicle
The following three systems help to control the vehicle
while driving — brakes, steering, and accelerator. At
times, as when driving on snow or ice, it is easy to ask
more of those control systems than the tires and road
can provide. Meaning, you can lose control of the
vehicle. See Traction ...