Why do some of the FPM100 pressure transducer accessories have a small plastic tube within the cable?

Some pressure transducers measure gauge pressure (pressure above atmospheric). These transducers have a small plastic vent tube enclosed in the connecting cable. Special care must be taken not to block or kink the vent tube, and not to expose the vent tube to moisture. The conducting wires of the pressure transducers can be extended up to 50 feet.