Take a wide mouthed bottle and stretch the nozzle of a ballon and clamp it on its mouth. Bound it also with the help of a rubber bandin such a way that the the ballon is fully stretched on the mouth of the bottle. Now take a drinking straw and attatch one end of it on the center of the stretched ballon with a glue. Then, continue to hold the straw in the same posotion till the glue gets dry. After accomplishing this, you have to do only one job more: to set a white strip of cardboard by the side of the bottle in such a way that it remains standing upright just behind the free end of the straw. Be wary to graduate this cardboard strip with the marks indicating 'high and low' degree signs.

Now your barometer is ready. As you know when the atmosphere prussere is high, it will excert similiar pressure in all directions. So much so that the pressure on all sides of the bottle. This in turn would put pressure on the attached end of the straw and its other end would rise higher to indicate the increase in pressure.

On the contrary, if the atmosphere pressure decreases, the ballon would not be deflated. But if the pressure becomes so low as to be even less than the air pressure inside the bottle. It will inflate the ballon and the free end on the straw, quite obviously, would indicate the decrease in pressure.

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