mmHgᵂ is "millimeters of Hg (Mercury)", a measure of vacuum. Originally defined as the extra pressure generated by a column of mercury one millimetre high, as read out by a Mercury pressure gauge.
ATMOSPHERIC PRESSURE nominal at sea level 760 mm Hg 29.9212 inches Hg 14.696 psi 1 bar
CONVERSIONᴳ TABLE mmHg inHg (inches of mercury) 560 22.0 600 23.6 10 0.39
NORMAL intake manifold vacuum 457-559 mm mercury 18-22 inches mercury
See also: Vacuum Gauge
Vacuum gauge reading in Inches (inHg)
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