A barometer is an instrument used to measure air pressure and track weather systems. The most common unit of measurement used in barometers is the millibar (mb).
A millibar is a form of metric measurement, with one millibar equaling one one-thousandth of a bar or 100 pascals, which is equivalent to one newton per square meter.
Millibars are used to measure atmospheric pressure or altitude. Normal atmospheric pressure measures 1,013.2 millibars.
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The two types of barometers are mercury and aneroid. In a mercury barometer, millibars measure how high the mercury column climbs a vertical glass tube. Aneroid barometers don’t use liquid of any kind, instead employing a flexible-walled evacuated capsule.
Aside from millibars, other units of measure used in barometers include pounds per square inch, pascals and inches of mercury.
A highly sensitive unit of measurement, one millibar indicates a change of one tenth of one percent in the atmospheric pressure.