Question

What's working principle of an Aneroid barometer??​

Answer 1

An aneroid barometer is built around a sealed box (blue, sometimes called an aneroid cell) that expands or contracts with increasing pressure

Answer 2

Inside an aneroid barometer is a small capsule. This capsule has had the air pumped out of it. When the air pressure rises, the sides of the capsule are compressed. The capsule is attached to levers which move a needle as the air pressure squeezes the capsule.