Barometers are used to measure atmospheric pressure, using the pressure exerted by the atmosphere by using water, air, or mercury. An aneroid barometer uses air.
Pressure tendency can forecast short term changes in the weather.
Numerous measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems, and frontal boundaries.
Isobars are lines showing areas of equal atmospheric pressure. When marked on a chart they show as acontour map of areas of high and low pressure.
Pressure can be measured in different ways, the most common is millibars. Calculations of pressure can also be made in Pascals or inches of mercury.
A barograph, (see right) which records a graph of some atmospheric pressure, uses an aneroid barometer mechanism to move a needle on a smoked foil or to move a pen upon paper, both of which are attached to a drum moved by clockwork.