How do you measure atmospheric pressure?

Atmospheric pressure is measured using a barometer, which can be either a mercury barometer or an aneroid barometer.

A mercury barometer consists of a glass tube filled with mercury, inverted in a mercury-filled basin. The atmospheric pressure pushes down on the mercury in the basin, causing the mercury in the tube to rise. The height of the mercury column, usually measured in millimetres of mercury (mmHg), indicates the atmospheric pressure. Standard atmospheric pressure at sea level is 760 mmHg.

An aneroid barometer, on the other hand, does not use liquid. It contains a small, flexible metal box called an aneroid cell. This cell is sealed and partially evacuated of air. Changes in atmospheric pressure cause the cell to expand or contract. These movements are mechanically amplified and displayed on a dial, usually in units of millibars (mb) or hectopascals (hPa), where 1 hPa equals 1 mb. Standard atmospheric pressure at sea level is 1013.25 hPa.

Both types of barometers are used to monitor weather conditions. For example, a falling barometer reading often indicates that a low-pressure system is approaching, which can bring bad weather. Conversely, a rising barometer reading suggests that a high-pressure system is on the way, usually associated with fair weather.

Understanding how to measure atmospheric pressure is crucial in meteorology, aviation, and even in everyday activities like hiking, where changes in pressure can affect weather predictions and altitude readings.