Measurement of Air Pressure

The atmosphere is held on the earth by the gravitational pull of the earth.
A column of air exerts weight in terms of pressure on the surface of the earth.
The weight of the column of air at a given place and time is called air pressure or atmospheric pressure.
Atmospheric pressure is measured by an instrument called barometer.
Nowadays Fortin’s barometer and Aneroid barometer are commonly used for measuring air pressure.
Atmospheric pressure is measured as force per unit area.
The unit used for measuring pressure is called millibar. Its abbreviation is ‘mb’.
One millibar is equal to the force of one gram per square centimetre approximately.
A pressure of 1000 millibars is equal to the weight of 1.053 kilograms per square centimetre at sea level.
It is equal to the weight of a column of mercury which is 76 centimetre high.
The international standard pressure unit is the “pascal”, a force of one Newton per square meter. In practice atmospheric pressure is expressed in kilopascals, (one kpa equals 1000 Pa).
The mean atmospheric pressure at sea level is 1013.25 millibars. However the actual pressure at a given place and at a given time fluctuates and it generally ranges between 950 and 1050 millibars.