Barometers Realm

At the heart of its mechanism lies a flattened, evacuated metal tube bent into a half-ring shape, with its ends connected to form a precise toothed rack that turns a gear attached to the pointer. An increase in atmospheric pressure causes the ends of the Bourdon tube to draw closer together, forming an almost perfect circle and moving the pointer to the right; a decrease in pressure causes the ends to move apart, resulting in the pointer’s movement to the left.