How does a banjo barometer work?

A banjo barometer works because of a small capsule or box made of beryllium and copper called an aneroid. In most designs, the aneroid box or capsule was on the back. Fluctuations in air pressure would cause the shape of the box or capsule to change, and this, in turn, moved the needle on the barometer dial. Shop a range of banjo barometers on 1stDibs.