Having a Rating Level as "No Rating" or "N/A"

Hi all,

Within our Performance Document set-ups, we are utilizing calculated ratings for our sections based upon an established 1-5 rating model, however one of the specifications is to allow the rater to be able to select "No Rating" in which the item should not affect the calculated scoring.

Currently, we have given it the value of '0', however, whenever it is selected, it brings the calculated scoring down rather than having no effect as intended.

Is there a way for us including a 'No Rating' or 'N/A' Rating Level without have it affect scoring?