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Many types of barometer makes for measuring air pressure.

More about weather instruments.

A barometer makes atmospheric pressure measurements.

This pressure tries to flatten you from of the weight of several miles of air above you - YES AIR DOES WEIGH SOMETHING.

How much? Imagine a vertical box on the shore of Long Island, 1 foot square, not very big, and going up to the top of the atmosphere, say, a few hundred miles. The downward force measurements of all the air in that box would weigh over 2000 pounds.

Air pressure science

Sea-level pressures range from 27" to 31" of mercury,

or about 95 to 105 kPa for you metric types. Higher air pressure weather includes increased sun, temperatures rising and lower winds. At the same time lower pressure is more frequently associated with different conditions. More cloud sky, rain or snow and wind power...

...And I won't even get into barometric pressure arthritis. If you live near big hills, these generalizations are not quite as reliable. Other features, called mesoscale patterns, can interfere with prevailing conditions.

Now, what do we use to measure the pressure?

Types of barometers.

A different type of barometer makes a different kind of measurement. Not just between digital barometers, stationary barometers and handheld barometers but we have more fundamental distinctions as well.

How far above level sea?

Nearly all barometer makes display the pressure and can be adjusted for altitude,

your position on elevation maps. Why? Because if you live in Denver, let's say, your atmospheric pressure will ALWAYS be lower than the pressure in Los Angeles, simply because your city is a mile in the air, so to speak.

Anyway, the adjustment is a simple one and gives you a reading of the pressure caused by the current weather system AS IF you were at sea level.

Most scientific barometer makes are electronic,

like those used in a environment-data logger project.

They consist of two gold electrodes configured as a capacitor inside a vacuum in which pressure causes deformation of the capsule and a change in the capacitance that is measured and converted into units of pressure.

Other types of barometer build and design specifications use simpler principles, and generally they respond to the changes of air pressure on a container with no air inside. Take a look at one of those glass water barometers, for instance.

These kinds of barometer makes, called altimeters, tell pilots how high their planes are.

Observers also use barometers to note pressure tendency. Has it gone up, down, remained steady, or any combination of these motions over the last three hours, and if so by how much.

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Barometer pictures and science gifts:

To find pictures of barometers, examine products listed on US or Canada eBay or a retail web page to see different kinds of barometer makes - including electronic, aneroid and liquid-filled models. Wikipedia will provide additional photos and information as well.

See the StuffInTheAir homepage to learn more about air and the weather.