Differential pressure transducer functioning

I do not quite understand how this device works and the book does not really explain anything that is easy to understand

I understand that a pressure difference at the ends of the device causes a change in capacitance due to the displacement of the dielectric material within the two capacitors but I can't understand what the book means by this balance of forces
VCDPT.PNGVCDPT3.PNGVCDPT2.PNG
 

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