Explanation:
Atmospheric pressure is the force exerted by the weight of the air in the atmosphere on a unit area. It is an important parameter in meteorology and is measured using a device called a barometer.

Barometer:
A barometer is a scientific instrument used to measure atmospheric pressure. It consists of a long glass tube that is closed at one end and open at the other end. The tube is filled with mercury, and the open end is submerged in a container of mercury. The pressure of the atmosphere pushes down on the surface of the mercury in the container, causing the mercury in the tube to rise.

Types of Barometers:
There are two main types of barometers:

1. Mercury Barometer:
- A mercury barometer is the traditional type of barometer that uses mercury as the measuring medium.
- The height of the mercury column in the tube is directly proportional to the atmospheric pressure.
- The standard atmospheric pressure at sea level is equal to the height of a mercury column that is approximately 760 millimeters (mm) tall.

2. Aneroid Barometer:
- An aneroid barometer is a more modern type of barometer that does not use a liquid.
- It consists of a metal box that is partially evacuated and has a flexible lid.
- When the atmospheric pressure changes, the metal box expands or contracts, causing the flexible lid to move.
- The movement of the flexible lid is then converted into a reading on a dial, indicating the atmospheric pressure.

Measurement Units:
The unit of measurement for atmospheric pressure is usually the Pascal (Pa) or the millibar (mb). Another common unit used is the millimeter of mercury (mmHg).

Conclusion:
In conclusion, atmospheric pressure is measured using a barometer. The barometer can be of the mercury or aneroid type, and it provides a measure of the force exerted by the weight of the air in the atmosphere. The measurement is usually given in units such as Pascal, millibar, or millimeter of mercury.