The sensor i have is vented to atmosphere and reads 2.9 - 36.9psi. Therefore it reads 14.7 psi (1.8v) at sea level.
What i was trying to say was, on power up, take a sample of the reading of surrounding atmospheric pressure and send the value to the eeprom. Use this value to set a display reading of 0psi. Offset all readings from this point forward with the eeprom value to provide an accurate representation of pressure applied relative to current atmospheric pressure.

Instruct the owner to undergo a calibration routine when the unit is first installed or if a sample can be taken quick enough, every time the unit is turned on before the engine is started.

The application is a turbo boost gauge. The sensor was selected because it was designed for this purpose and i have seen a working gauge using this sensor.
If i get adventurous enough, there will be a vacuum reading too.

Does this clear things up a little??

Regards,

James.