- probably like 10.5v
This value at A0-pin is not acceptable when the VREF (Full Scale) of the ADC is 5V.
Calibration is an important issue to bring down your Pressure Readings into human readable range!
Every system is a Real System, and it has gain and offset. We need to make a two-point calibration to find these parameters in order to derive the response equation -- y = mx + c.