Thank you for your question.  DAU does not write contracts, so we do not have access to any of the fielded contract writing systems to be able to replicate your question.  Having said that, we have numerous staff who have worked in

PD2 prior to arrival at DAU.  Based on what you describe, you should be able to press and hold shift, and double click to display a pop-up list of entries to populate the data element.  My recollection is this field simply refers to Origin or Destination.  If none of this guidance is correct, I would recommend you work with your PD2 Super User or System Administrator to obtain a current copy of the PD2 Concept of Operations (CONOPS).  This is an extensive reference that discusses each field in PD2, and would have more specific guidance for this.