This aneroid barometer consists of a cylindrical metal container, closed at the back and sides, with a dial, pointers and a glass cover on the front. Mounted behind the dial is a mechanism that includes a metal capsule with flexible sides. The capsule contains a small amount of air. As air pressure increases, the capsule's walls contract. Even the slightest change in air pressure changes the thickness of the capsule. As the atmospheric pressure increases, the capsule's volume of air gets compressed. To record this change in atmospheric pressure, one end of the capsule is fastened to a pointer by a series of levers and pulleys. As the volume of air inside the capsule changes, the pointer moves. Marked in both millibars and millimeters.