Inch of Mercury

Inch of Mercury (inHg) is a British and American unit of measure for pressure. 1 inHg at 0°C (32°F) equals 3386.39 pascals. An inHg at 0°C is defined as the pressure exerted by a column of mercury with a density of 13,595.1 kg/m3 under the pull of gravity at 9.80665 m/s2.
The inHg pressure unit is not used so extensively in the UK anymore and has been mostly replaced by the metric units mmHg and mbar. However, inches of Mercury are still used extensively in the USA particularly for meteorological purposes when measuring atmospheric pressure.

Mercury has a very high density which makes it a very practical liquid for use inside fluid filled columns for measuring pressure in the laboratory. However Mercury is now considered a hazardous substance and mercury manometers have been almost totally eliminated from laboratories for health and safety reasons.