mm Hg

mm Hg 'mil-ə-.mēt-ər-əv-'mər-kyə-rē, -k(ə-)rē n a unit of pressure equal to the pressure exerted by a column of mercury 1 millimeter high at 0°C and under the acceleration of gravity and nearly equivalent to 1 torr (about 133.3 pascals)

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millimeter of mercury, a unit of pressure equal to that exerted by a column of mercury at 0°C one millimeter high at standard gravity. It is equal to 1 torr, or 133.3 pascals.