The Collaborative International Dictionary of English v.0.48:

Exactness \Ex*act"ness\, n.
   1. The condition of being exact; accuracy; nicety; precision;
      regularity; as, exactness of judgement or deportment.
      [1913 Webster]

   2. Careful observance of method and conformity to truth; as,
      exactness in accounts or business.
      [1913 Webster]

            He had . . . that sort of exactness which would have
            made him a respectable antiquary.     --Macaulay.
      [1913 Webster]

WordNet (r) 3.0 (2006):

exactness
    n 1: the quality of being exact; "he demanded exactness in all
         details"; "a man of great exactitude" [syn: exactness,
         exactitude] [ant: inexactitude, inexactness]