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.
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.