inHg stands for inches of mercury, which is a unit of measurement commonly used to express atmospheric pressure. The term originates from the way barometric pressure is historically measured using a mercury barometer. In such devices, the height of mercury in a column is used to determine the pressure of the atmosphere above it.
One inch of mercury is defined as the pressure exerted by a column of mercury exactly one inch high, under the influence of gravity. This measurement is critical in various fields, including meteorology, aviation, and even in some medical applications, like blood pressure measurement.
In meteorology, for example, standard atmospheric pressure at sea level is about 29.92 inHg. Variations in inHg readings can indicate changes in weather conditions, such as the approach of a storm or fair weather. The unit is particularly favored in the United States, while other countries might use different units, such as pascals or millibars, for the same purpose.