Describe the working principle of an aneroid barometer.

An aneroid barometer has a corrugated metal box which is made air tight by pumping air out of it and completely sealed. It has a thin flexible lid which is sensitive to changes of air pressure. The lid is pressed inward or outward as the air pressure increases or decreases respectively. The inward or outward movement of the lid moves a system of levers which is connected to a pointer. The pointer moves over the graduated dial to give the reading of the atmospheric pressure.