Figure 2

Line (A) joins the gingival zeniths of the central incisor and canine. Line (B) marks the gingival zenith of the lateral incisor. In this case, line B was located below line (A) and so is marked as negative.
Line (A) joins the gingival zeniths of the central incisor and canine. Line (B) marks the gingival zenith of the lateral incisor. In this case, line B was located below line (A) and so is marked as negative.