The C-shaped Bourdon tube has a hollow, elliptical cross section
It is closed at one end and is connected to the socket at the other
When pressure is applied, its cross section becomes more circular, causing the tube to straighten until the force of the pressure is balanced by the resistance of the tube material
A pointer is attached to the closed end of the tube through a linkage arm, a gear & pinion assembly, which rotates the pointer around a graduated scale