How is the transducer brought to a specifed pressure?

The positive port is connected to the PUSH side of the piston causing a positive pressure. The low port is connected to the back side of the piston causing a vacuum in the low port. The pressure and vacuum are not necessarily equal in opposite values, due to the difference between the volumes on either side of the piston. The only result you can rely on is the differential value.

Example of a 2" differential: If the piston was exactly centered then the positive pressure port would be at +1" and the low port would be at -1". Since this is not always the case, one port could be at +1.2" and the other at -0.8" which would provide a 2" differential.