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By and large barometers are of three types. They are easily available in market: 1)Water-based barometers- Water-based barometers are made of a glass container with a sealed body, half filled with water. It has a narrow spout which is connected to the body below the water level and rises again above the water level where it is open to the atmosphere.
2) Mercury barometers The standard mercury barometer has a glass column measuring about 30 inches in height, is closed at one end and has and unless the weight of the mercury column balances the atmospheric force exerted on the reservoir. They are available in number of designs in order to make them simpler to read, and easier to transport. 3) Aneroid barometer The modern aneroid barometer has a small and flexible metal box called an aneroid capsule which is made from an alloy of beryllium and copper. This metal box is tightly sealed once the air is removed from it. Then the small external change results in expansion or contraction of mechanical levers and devices which are displayed on the face of the aneroid barometer. They are several models available with manually set needle which can mark measurement which represents a change.
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