Saturn 2007 Ion Owner's Manual page 181

If your vehicle has this gage, it is located on the
steering column.
This gage indicates vacuum during light to
moderate throttle and boost under heavier throttle.
This gage displays the air pressure level in the
intake manifold before it enters the engine's
combustion chamber.
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This gage is automatically centered at zero every
time the ignition is turned to RUN. Actual
vacuum or boost is displayed from this zero point.
The boost gage has three pairs of lights that
are located on each side of the gage. These lights
are used to indicate three different engine rpm
levels. The default setting for the lower pair
of lights is 4,400 rpm, the middle pair of lights is
5,600 rpm, and the top pair of lights is 6,200 rpm.
These settings can be adjusted by turning the
stem behind each light. To have the light
pair come on at a higher rpm level, turn the stem
counterclockwise. To have the light pair come
on at a lower rpm level, turn the stem clockwise.
Each detent adjusts the settings by 100 rpm.
To restore the default settings, press and hold any
stem for three seconds. The lights will flash
three times.
To turn the lights off or on, press and release
any stem.
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