Spring tube manometer cross-section why oval

Tube cross-section is oblate or oval, when the spring bend by the role of medium pressure, its cross-section will have a tendency to become round, forcing the spring bend gradually straighten the spring bend, so that the free end of the spring bend upward. Because the oval cross-section in the media pressure will tend to round, so that the spring tube bent into a circular arc with the production of outward straightening expansion of deformation, so that the free end of the spring tube to produce displacement, and the displacement of the free end of the free end of the pressure to be measured in a certain range of a certain linear correlation between. Therefore, the displacement of the free end of the spring tube through the appropriate amplification, can indicate the size of the measured medium pressure.