anchor.diff:              tlen = sqrt(taup(1)**2 + taup(2)**2 + taup(3)**2)
   
               DO m = 1,3
  -               xtangents(i,j,m) = taup(m)/tlen
  +c               xtangents(i,j,m) = taup(m)/tlen
  +               xtangents(i,j,m) = taup(m)
               ENDDO
               edge_lengths(i,j,1) = tlen
            ENDDO
  
positive.code: 
  c           # nv has unit length
              do m = 1,3
                 ytangents(i,j,m) = taup(m)/tlen
              enddo
              edge_lengths(i,j,2) = tlen
           enddo
  
negative.code:             area(i,j) = sum_area
           enddo
        enddo
  
        end
  
  