Billysugger:
Your sensor is an absolute pressure sensor, it is not suitable for differential pressure measurement. You need a differential pressure sensor.
alas, I was wrong. the absolute pressure sensor in the OP link has the differential sensing element sealed chamber that was not open to the atmosphere.
although the fundamental principal is that all sensors are differential, this device has one side sealed to create a reference chamber.
since a new sensor is needed, the choices of buying one that has two ports for tubing or buying one that has one port for tubing and the other side open to atmospheric pressure, the dual port would be the same cost and unless the measurement WAS for pressure comparison between atmospheric and some device, the dual port would be the better choice.